Fix crash when minimizing game window (#933)

Returns early if the window or framebuffer width or height = 0 to avoid dividing by zero. Checked the vector components individually instead of using `Vector2i.Equals()` because you can end up in a situation where width is non-zero and height is zero if you manually resize the window instead of using the minimize button.

Robust.Client/Graphics/Clyde/Clyde.Windowing.cs

@@ -292,8 +292,11 @@ namespace Robust.Client.Graphics.Clyde
             var oldSize = _framebufferSize;
             GLFW.GetFramebufferSize(window, out var fbW, out var fbH);
             _framebufferSize = (fbW, fbH);
-
             _windowSize = (width, height);
+
+            if(fbW == 0 || fbH == 0 || width == 0 || height == 0)
+                return;
+
             _pixelRatio = _framebufferSize / _windowSize;
 
             GL.Viewport(0, 0, fbW, fbH);