Caused by rB3e4d720ae483: Fix logical error resolving RNA paths.

Before above commit, this had a different path handling and
RNA_path_from_ID_to_struct() was always used [which kind of took care of
this]. Now this is only used if ptr represents an ID itself, so we are
"loosing" part of the path.

This patch adds the path back on the member_id in
wm_context_member_from_ptr() for everthing related to space_data, so
WM_context_path_resolve_property_full() can construct a full path even
for these.

Other possibility would be to use RNA_path_from_ID_to_struct() even for
the cases in WM_context_path_resolve_property_full() that would
previously just copy the blank member_id into member_id_data_path. This
would probably be more general (and also a bit more like it was before
the culprit commit)? But dropping this solution here since
@Campbell Barton (campbellbarton) said this is probably the way to go.