Handle case of no available CRTCs.

README.md

@@ -50,6 +50,8 @@ The following dependencies are needed by the examples and test programs:
  - [Cocoa] Bugfix: Using a 1x1 cursor for hidden mode caused some screen
                    recorders to fail
  - [X11] Bugfix: The case of finding no usable CRTCs was not detected
+ - [X11] Bugfix: Detection of broken Nvidia RandR gamma support did not verify
+                 that at least one CRTC was present
 
 
 ## Contact

src/x11_gamma.c

@@ -43,10 +43,12 @@ void _glfwInitGammaRamp(void)
         XRRScreenResources* rr = XRRGetScreenResources(_glfw.x11.display,
                                                        _glfw.x11.root);
 
-        if (XRRGetCrtcGammaSize(_glfw.x11.display, rr->crtcs[0]) == 0)
+        if (!rr->ncrtc || !XRRGetCrtcGammaSize(_glfw.x11.display, rr->crtcs[0]))
         {
             // This is probably older Nvidia RandR with broken gamma support
             // Flag it as useless and fall back to Xf86VidMode, if available
+            _glfwInputError(GLFW_PLATFORM_ERROR,
+                            "X11: RandR gamma ramp support seems broken");
             _glfw.x11.randr.gammaBroken = GL_TRUE;
         }