Explicitly cast to a uint to fix a compile error

When using QtTest inside the notification example for QtAndroidExtras
there as a problem with the compilation as it saw it as being an ambiguous
check. Therefore doing an explicit case to uint ensures it is not a
problem.

Change-Id: Ibc9ce4c64292bf5ae7c501c592d8c42a66934b8b
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

src/testlib/qtestmouse.h

@@ -98,7 +98,7 @@ namespace QTest
             mouseEvent(MouseRelease, window, button, stateKey, pos);
             return;
         }
-        QTEST_ASSERT(stateKey == 0 || stateKey & Qt::KeyboardModifierMask);
+        QTEST_ASSERT(uint(stateKey) == 0 || stateKey & Qt::KeyboardModifierMask);
 
         stateKey &= static_cast<unsigned int>(Qt::KeyboardModifierMask);