qGlobalQHashSeed: initialize the seed before returning it

If you had never used QHash before, this function returned -1. That's
not useful if you're trying to implement your own QHash that uses Qt's
global seed.

Change-Id: Ib0e40a7a3ebc44329f23fffd14b2e875b970a55c
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/corelib/tools/qhash.cpp

@@ -361,6 +361,7 @@ static void qt_initialize_qhash_seed()
  */
 int qGlobalQHashSeed()
 {
+    qt_initialize_qhash_seed();
     return qt_qhash_seed.load();
 }