[Bug fortran/67567] resolve.c: gfc_error called with iface->module == NULL

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67567

--- Comment #3 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Vittorio Zecca from comment #2)
> Unfortunately I do not master gdb and gcc internals enough for that.
> The check costs two instructions on my x86-64.

Two instructions that we do not need to execute! :)

In this case, the worst part is that it will hide a bug in error reporting. It
will print something like:

Error: X between the MODULE PROCEDURE declaration in module  and the
declaration at (1) in SUBMODULE Y

which is wrong.