Early-exit InitWindow if InitGraphicsDevice fails

Otherwise we may run into LoadDefaultFont and crash in rlLoadTexture
Also moves InitTimer() before InitGraphicsDevice(), to allow it to be
tested even if InitWindow ultimately fails.

src/core.c

@@ -441,12 +441,13 @@ void InitWindow(int width, int height, void *data)
     uwpWindow = (EGLNativeWindowType)data;
 #endif
 
+    // Init hi-res timer
+    InitTimer();
+
     // Init graphics device (display device and OpenGL context)
     // NOTE: returns true if window and graphic device has been initialized successfully
     windowReady = InitGraphicsDevice(width, height);
-
-    // Init hi-res timer
-    InitTimer();
+    if (!windowReady) return;
 
 #if defined(SUPPORT_DEFAULT_FONT)
     // Load default font