Fix memory leak

Destroy the QDBusPendingCallWatcher object when received
the QDBusPendingCallWatcher::finished signal later.

Pick-to: 5.15 6.2
Change-Id: I1ec67bf7c286f38200c374ad92df2a1579588a8a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/plugins/platformthemes/xdgdesktopportal/qxdgdesktopportalfiledialog.cpp

@@ -302,6 +302,7 @@ void QXdgDesktopPortalFileDialog::openPortal()
                                                   this,
                                                   SLOT(gotResponse(uint,QVariantMap)));
         }
+        watcher->deleteLater();
     });
 }
 

src/plugins/platformthemes/xdgdesktopportal/qxdgdesktopportaltheme.cpp

@@ -111,6 +111,7 @@ QXdgDesktopPortalTheme::QXdgDesktopPortalTheme()
         if (reply.isValid()) {
             d->fileChooserPortalVersion = reply.value().toUInt();
         }
+        watcher->deleteLater();
     });
 }