Prevent infinite recursion with Qt >5.15.2

The fix for QTBUG-87781 is to recreate an internal mapping in
QSortFilterProxyModel::setSourceModel(), and KisResourceModel calls
this in the constructor.
This leads to KisResourceModel::filterAcceptsRow() being called, which
ultimately fetches data via KisResourceQueryMapper::variantFromResourceQuery().
So the latter must not create a temporary KisResourceModel when processing the
data role used by filterAcceptsRow().

So only create the temporary model when actually required.

libs/resources/KisResourceQueryMapper.cpp

@@ -20,7 +20,6 @@
 QVariant KisResourceQueryMapper::variantFromResourceQuery(const QSqlQuery &query, int column, int role)
 {
     const QString resourceType = query.value("resource_type").toString();
-    KisResourceModel resourceModel(resourceType);
 
     switch(role) {
     case Qt::DisplayRole:
@@ -107,6 +106,7 @@ QVariant KisResourceQueryMapper::variantFromResourceQuery(const QSqlQuery &query
         return query.value("resource_type");
     case Qt::UserRole + KisAbstractResourceModel::Tags:
     {
+        KisResourceModel resourceModel(resourceType);
         QStringList tagNames;
         Q_FOREACH(const KisTagSP tag, resourceModel.tagsForResource(query.value("id").toInt())) {
             tagNames << tag->name();
@@ -124,6 +124,7 @@ QVariant KisResourceQueryMapper::variantFromResourceQuery(const QSqlQuery &query
         }
         else {
             // Now we have to check the resource, but that's cheap since it's been loaded in any case
+            KisResourceModel resourceModel(resourceType);
             KoResourceSP resource = resourceModel.resourceForId(query.value("id").toInt());
             return resource->isDirty();
         }