winemac: When ClipCursor() is called redundantly, don't warp the cursor or discard mouse move events.

Fixes a problem in some games which repeatedly (re)establish the same cursor
clipping rect, making it exceedingly difficult to move the camera with the
mouse.

dlls/winemac.drv/cocoa_app.m

@@ -1353,6 +1353,10 @@ - (BOOL) startClippingCursor:(CGRect)rect
         if (!cursorClippingEventTap && ![self installEventTap])
             return FALSE;
 
+        if (clippingCursor && CGRectEqualToRect(rect, cursorClipRect) &&
+            CGEventTapIsEnabled(cursorClippingEventTap))
+            return TRUE;
+
         err = CGAssociateMouseAndMouseCursorPosition(false);
         if (err != kCGErrorSuccess)
             return FALSE;