tst_QGlobal: fix -Wmaybe-uninitialized

GCC 14 doesn't understand that neither q_check_ptr() nor
qCompare<int*> dereference the pointer.

Since the missing initialization isn't part of the test (except,
maybe, to provoke this warning if the implementation indeed changed to
dereference the pointer), fix by initializing the int, like we do for
the string a few lines below.

Amends the start of the public history.

Pick-to: 6.8 6.7 6.5 6.2 5.15
Change-Id: I6033e026f041b03821b776daa8e65586b8054136
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/corelib/global/qglobal/tst_qglobal.cpp

@@ -261,7 +261,7 @@ void tst_QGlobal::qtry()
 
 void tst_QGlobal::checkptr()
 {
-    int i;
+    int i = 0;
     QCOMPARE(q_check_ptr(&i), &i);
 
     const char *c = "hello";