Fixes #8992, ResourceGroup save dialog not closing

This problem seems (at least in my case) only to occur because of VersionX but the cause is a bug in the core...that is the create resource group processor mistakenly is calling OnChunkFormSave instead of OnResourceGroupSave which then triggers the VersionX plugin and then calls ->toArray() on a non-object, which let the whole thing fail...the fix is very simple, but I think this should not be delayed till 2.3 (which is the target version for #8992)!

Fix also provided for VersionX (for older MODX versions in case of merge)