Fix warning on invalid time-zone lookup

Amends commit 569dc0de50 to still return
when no zone file is found with the given name, as the code did
before.  Attempting to continue past the error was provoking warnings
from QIODevice::read().

Pick-to: 6.6.0 6.6 6.5
Task-number: QTBUG-116017
Change-Id: I0e224a6b30a3f32cd925d87ffba4dcb24f9b8568
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/time/qtimezoneprivate_tz.cpp

@@ -803,8 +803,8 @@ QTzTimeZoneCacheEntry QTzTimeZoneCache::findEntry(const QByteArray &ianaId)
         if (check.isValid) {
             ret.m_hasDst = check.hasDst;
             ret.m_posixRule = ianaId;
-            return ret;
         }
+        return ret;
     }
 
     QDataStream ds(&tzif);