Edit of a PDS or PDSE (as opposed to a member) should fail or show a list of members

[MikeFultonDev]

This is opened from a report in: #68

Edit a PDS by mistake
vim "//'@02858.t.cntl'"

@IgorTodorovskiIBM we probably need more 'handshaking' for this scenario and it is also related to: #73 but perhaps we at least fail the edit as a starting point.

[MikeFultonDev]

@IgorTodorovskiIBM for now, I think a reasonable fix would be for you to check the information on the dataset after the open, and if it's a PDSE or PDS and no member was specified, to fail, e.g.

struct DFILE* dsfile = open_dataset(ffname, NULL);
...
if ((dsfile->dsorg == D_PDSE || dsfile->dsorg == D_PDS) && has_member(dsfile->difile)) {
   error
}

We need to expose the has_member function for this - and probably that can be at the dsfile level.
I don't think it makes sense to put this into libdio because for other uses, the user may want to read the pds member (e.g. to get the directory information for the pds).

Thoughts?

[IgorTodorovskiIBM]

Agree, I have added the code in 2149fe0 and zopencommunity/libdio@fcabd76. It will be available in the next release of vim%datasetio