Backends: GLFW: workaround for cases where glfwGetMonitorWorkarea fails (#3457)

examples/imgui_impl_glfw.cpp

@@ -442,16 +442,16 @@ static void ImGui_ImplGlfw_UpdateMonitors()
         int x, y;
         glfwGetMonitorPos(glfw_monitors[n], &x, &y);
         const GLFWvidmode* vid_mode = glfwGetVideoMode(glfw_monitors[n]);
+        monitor.MainPos = monitor.WorkPos = ImVec2((float)x, (float)y);
+        monitor.MainSize = monitor.WorkSize = ImVec2((float)vid_mode->width, (float)vid_mode->height);
 #if GLFW_HAS_MONITOR_WORK_AREA
-        monitor.MainPos = ImVec2((float)x, (float)y);
-        monitor.MainSize = ImVec2((float)vid_mode->width, (float)vid_mode->height);
         int w, h;
         glfwGetMonitorWorkarea(glfw_monitors[n], &x, &y, &w, &h);
-        monitor.WorkPos = ImVec2((float)x, (float)y);;
-        monitor.WorkSize = ImVec2((float)w, (float)h);
-#else
-        monitor.MainPos = monitor.WorkPos = ImVec2((float)x, (float)y);
-        monitor.MainSize = monitor.WorkSize = ImVec2((float)vid_mode->width, (float)vid_mode->height);
+        if (w > 0 && h > 0) // Workaround a small GLFW issue reporting zero on monitor changes: https://github.com/glfw/glfw/pull/1761
+        {
+            monitor.WorkPos = ImVec2((float)x, (float)y);
+            monitor.WorkSize = ImVec2((float)w, (float)h);
+        }
 #endif
 #if GLFW_HAS_PER_MONITOR_DPI
         // Warning: the validity of monitor DPI information on Windows depends on the application DPI awareness settings, which generally needs to be set in the manifest or at runtime.