grantleetheme: check for a null pointer

pkgs/applications/kde/grantleetheme.nix

···
     license = with lib.licenses; [ gpl2 lgpl21 fdl12 ];
     maintainers = kdepimTeam;
   };
+  output = [ "out" "dev" ];
+  patches = [ ./grantleetheme_check_null.patch ];
   nativeBuildInputs = [ extra-cmake-modules kdoctools ];
   buildInputs = [
     grantlee5 ki18n kiconthemes knewstuff kservice kxmlgui qtbase
   ];
-  output = [ "out" "dev" ];
+  propagatedBuildInputs = [ grantlee5 kiconthemes knewstuff ];
 }

pkgs/applications/kde/grantleetheme_check_null.patch

···
+diff --git a/src/grantleetheme.cpp b/src/grantleetheme.cpp
+index b86fc3a..8af72f4 100644
+--- a/src/grantleetheme.cpp
++++ b/src/grantleetheme.cpp
+@@ -102,7 +102,10 @@ QString ThemePrivate::errorTemplate(const QString &reason,
+     Grantlee::Context ctx = createContext();
+     ctx.insert(QStringLiteral("error"), reason);
+     ctx.insert(QStringLiteral("templateName"), origTemplateName);
+-    ctx.insert(QStringLiteral("errorMessage"), failedTemplate->errorString());
++    const QString errorString = failedTemplate
++            ? failedTemplate->errorString()
++            : QStringLiteral("(null template)");
++    ctx.insert(QStringLiteral("errorMessage"), errorString);
+     return tpl->render(&ctx);
+ }
+ 
+@@ -208,7 +211,7 @@ QString Theme::render(const QString &templateName, const QVariantHash &data, con
+     }
+ 
+     Grantlee::Template tpl = d->loader->loadByName(templateName, ThemePrivate::sEngine);
+-    if (tpl->error()) {
++    if (!tpl || tpl->error()) {
+         return d->errorTemplate(i18n("Template parsing error"), templateName, tpl);
+     }
+