Fixed invalid video mode being restored.

src/cocoa_monitor.m

@@ -200,10 +200,8 @@ GLboolean _glfwSetVideoMode(_GLFWmonitor* monitor, const GLFWvidmode* desired)
             monitor->ns.previousMode = CGDisplayCopyDisplayMode(monitor->ns.displayID);
 
         CGDisplayFadeReservationToken token = beginFadeReservation();
-
         CGDisplayCapture(monitor->ns.displayID);
         CGDisplaySetDisplayMode(monitor->ns.displayID, native, NULL);
-
         endFadeReservation(token);
     }
 
@@ -223,13 +221,18 @@ GLboolean _glfwSetVideoMode(_GLFWmonitor* monitor, const GLFWvidmode* desired)
 // Restore the previously saved (original) video mode
 //
 void _glfwRestoreVideoMode(_GLFWmonitor* monitor)
+{
+    if (monitor->ns.previousMode)
     {
         CGDisplayFadeReservationToken token = beginFadeReservation();
-
-    CGDisplaySetDisplayMode(monitor->ns.displayID, monitor->ns.previousMode, NULL);
+        CGDisplaySetDisplayMode(monitor->ns.displayID,
+                                monitor->ns.previousMode, NULL);
         CGDisplayRelease(monitor->ns.displayID);
-
         endFadeReservation(token);
+
+        CGDisplayModeRelease(monitor->ns.previousMode);
+        monitor->ns.previousMode = NULL;
+    }
 }