[libqofono] Synchronously requested QOfonoManager must be up to date.…

… JB#51589

If QOfonoManager::instance() is invoked first and the modem query
hasn't completed yet, QOfonoManager::instance(true) would return an
instance without the modem list. That's not right.

Explicit intention to block must guarantee that the returned
instance if fully up to date.

src/qofonomanager.cpp

@@ -276,7 +276,9 @@ QSharedPointer<QOfonoManager> QOfonoManager::instance(bool mayBlock)
     if (mgr.isNull()) {
         mgr = QSharedPointer<QOfonoManager>(new QOfonoManager(mayBlock), &QObject::deleteLater);
         sharedInstance = mgr;
-    } else {
+    } else if (mayBlock) {
+        // Make sure that modems are available
+        mgr->getModems();
     }
     return mgr;
 }