x11: Catch X11 errors in X11_SetWindowPosition and X11_SetWindowSize.

The functions can go south if other operations are in progress, like
X11_SetWindowBordered, which might be doing something traumatic behind the
scenes of the window manager.

We can't make these tasks totally synchronous, which would fix the problem,
because not only can the window manager block however long it wants, it might
also decide to deny our requests without any notification, so we'd be waiting
forever for a window change that isn't coming.  :(

Fixes #5274.

src/video/x11/SDL_x11window.c

@@ -782,11 +782,22 @@ X11_SetWindowIcon(_THIS, SDL_Window * window, SDL_Surface * icon)
     X11_XFlush(display);
 }
 
+static SDL_bool caught_x11_error = SDL_FALSE;
+static int
+X11_CatchAnyError(Display * d, XErrorEvent * e)
+{
+    /* this may happen during tumultuous times when we are polling anyhow,
+        so just note we had an error and return control. */
+    caught_x11_error = SDL_TRUE;
+    return 0;
+}
+
 void
 X11_SetWindowPosition(_THIS, SDL_Window * window)
 {
     SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
     Display *display = data->videodata->display;
+    int (*prev_handler) (Display *, XErrorEvent *) = NULL;
     unsigned int childCount;
     Window childReturn, root, parent;
     Window* children;
@@ -805,20 +816,27 @@ X11_SetWindowPosition(_THIS, SDL_Window * window)
 
     /* Wait a brief time to see if the window manager decided to let this move happen.
        If the window changes at all, even to an unexpected value, we break out. */
+    X11_XSync(display, False);
+    prev_handler = X11_XSetErrorHandler(X11_CatchAnyError);
+
     timeout = SDL_GetTicks() + 100;
     while (SDL_TRUE) {
         int x, y;
+
+        caught_x11_error = SDL_FALSE;
         X11_XSync(display, False);
         X11_XGetWindowAttributes(display, data->xwindow, &attrs);
         X11_XTranslateCoordinates(display, parent, DefaultRootWindow(display),
                                   attrs.x, attrs.y, &x, &y, &childReturn);
 
-        if ((x != orig_x) || (y != orig_y)) {
-            window->x = x;
-            window->y = y;
-            break;  /* window moved, time to go. */
-        } else if ((x == window->x) && (y == window->y)) {
-            break;  /* we're at the place we wanted to be anyhow, drop out. */
+        if (!caught_x11_error) {
+            if ((x != orig_x) || (y != orig_y)) {
+                window->x = x;
+                window->y = y;
+                break;  /* window moved, time to go. */
+            } else if ((x == window->x) && (y == window->y)) {
+                break;  /* we're at the place we wanted to be anyhow, drop out. */
+            }
         }
 
         if (SDL_TICKS_PASSED(SDL_GetTicks(), timeout)) {
@@ -827,6 +845,9 @@ X11_SetWindowPosition(_THIS, SDL_Window * window)
 
         SDL_Delay(10);
     }
+
+    X11_XSetErrorHandler(prev_handler);
+    caught_x11_error = SDL_FALSE;
 }
 
 void
@@ -892,6 +913,7 @@ X11_SetWindowSize(_THIS, SDL_Window * window)
 {
     SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
     Display *display = data->videodata->display;
+    int (*prev_handler) (Display *, XErrorEvent *) = NULL;
     XWindowAttributes attrs;
     int orig_w, orig_h;
     Uint32 timeout;
@@ -943,19 +965,25 @@ X11_SetWindowSize(_THIS, SDL_Window * window)
         X11_XResizeWindow(display, data->xwindow, window->w, window->h);
     }
 
+    X11_XSync(display, False);
+    prev_handler = X11_XSetErrorHandler(X11_CatchAnyError);
+
     /* Wait a brief time to see if the window manager decided to let this resize happen.
        If the window changes at all, even to an unexpected value, we break out. */
     timeout = SDL_GetTicks() + 100;
     while (SDL_TRUE) {
+        caught_x11_error = SDL_FALSE;
         X11_XSync(display, False);
         X11_XGetWindowAttributes(display, data->xwindow, &attrs);
 
-        if ((attrs.width != orig_w) || (attrs.height != orig_h)) {
-            window->w = attrs.width;
-            window->h = attrs.height;
-            break;  /* window changed, time to go. */
-        } else if ((attrs.width == window->w) && (attrs.height == window->h)) {
-            break;  /* we're at the place we wanted to be anyhow, drop out. */
+        if (!caught_x11_error) {
+            if ((attrs.width != orig_w) || (attrs.height != orig_h)) {
+                window->w = attrs.width;
+                window->h = attrs.height;
+                break;  /* window changed, time to go. */
+            } else if ((attrs.width == window->w) && (attrs.height == window->h)) {
+                break;  /* we're at the place we wanted to be anyhow, drop out. */
+            }
         }
 
         if (SDL_TICKS_PASSED(SDL_GetTicks(), timeout)) {
@@ -964,6 +992,9 @@ X11_SetWindowSize(_THIS, SDL_Window * window)
 
         SDL_Delay(10);
     }
+
+    X11_XSetErrorHandler(prev_handler);
+    caught_x11_error = SDL_FALSE;
 }
 
 int