flatpak: Do not call flatpak function with a nullptr

BUG: 445819


(cherry picked from commit 98aced4c)

libdiscover/backends/FlatpakBackend/FlatpakJobTransaction.cpp

@@ -61,7 +61,7 @@ void FlatpakJobTransaction::finishTransaction()
         m_app->setState(AbstractResource::None);
     }
 
-    if (!m_appJob->errorMessage().isEmpty()) {
+    if (!m_appJob->cancelled() && !m_appJob->errorMessage().isEmpty()) {
         Q_EMIT passiveMessage(m_appJob->errorMessage());
     }
 

libdiscover/backends/FlatpakBackend/FlatpakResource.cpp

@@ -608,7 +608,9 @@ QString FlatpakResource::versionString()
     }
     if (isInstalled()) {
         auto ref = qobject_cast<FlatpakBackend *>(backend())->getInstalledRefForApp(this);
-        version = flatpak_installed_ref_get_appdata_version(ref);
+        if (ref) {
+            version = flatpak_installed_ref_get_appdata_version(ref);
+        }
     } else if (!m_appdata.releases().isEmpty()) {
         auto release = m_appdata.releases().constFirst();
         version = release.version();