Avoid "<Error>: clip: empty path" messages

Change-Id: I6f640c0c4459f8330261ca59145a10b7a624bbe8

vcl/coretext/salgdi2.cxx

@@ -897,8 +897,8 @@ bool SvpSalGraphics::CheckContext()
             }
         }
 
-        CGContextClip(mrContext);
-
+        if (!CGContextIsPathEmpty(mrContext))
+            CGContextClip(mrContext);
     }