tst_QRect: drop a test that depends on int overflow

The compiler can statically check that this is undefined
behavior:

  tst_qrect.cpp:3173:52: warning: integer overflow in expression [-Woverflow]
               << QRect(QPoint(0,0), QPoint(INT_MAX+(0-INT_MIN),INT_MAX+(0-INT_MIN)));
                                                   ~^~
  tst_qrect.cpp:3173:72: warning: integer overflow in expression [-Woverflow]
               << QRect(QPoint(0,0), QPoint(INT_MAX+(0-INT_MIN),INT_MAX+(0-INT_MIN)));
                                                                       ~^~

Fix by skipping the test (like most of the others are
in the block).

Change-Id: I359a5e16db6c660c9f11d7dd8fbb40730bd63887
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>