This was reported in the form of the eyedropper of the 'Parent' property
creating a custom property 'parent' if self was picked.

Problem arises when certain checks for setting rna pointer properties
failed (for example: the PROP_ID_SELF_CHECK check) and then a different
code path was entered (which was only meant for IDProperties).

Problem was introduced in rBa7b3047cefcb.

To solve, now first enter the branch for rna-based pointer properties,
then perform the sanity-checks (and if these fail: dont enter the other
unrelated codepath but instead do nothing)