Initialize the expiryTimeoutSeconds variable in CacheableObject

The variable expiryTimeoutSeconds is set by the function
QNetworkAccessCache::addEntry and as a parameter is defaulted to -1
so initialize it to -1 with NSDMI.

Task-number: QTBUG-125026
Pick-to: 6.7 6.5
Change-Id: I8a96c2acbf94be409529200801d4d7169e852ac1
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit 9e75236a0dd157ca85e6f38870fac37214b683b2)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/network/access/qnetworkaccesscache_p.h

@@ -43,7 +43,7 @@ public:
         QByteArray key;
         bool expires;
         bool shareable;
-        qint64 expiryTimeoutSeconds;
+        qint64 expiryTimeoutSeconds = -1;
     public:
         CacheableObject();
         virtual ~CacheableObject();