The fix to the PR probably counts as obvious, but here it is, along
with a testcase.  Changelogs below.

Regtested on i686-pc-linux-gnu.

Whoever reviews this, please feel free to commit.

Thanks,
Harald


2018-03-02  Harald Anlauf  <anlauf@gmx.de>

	PR fortran/71085
	* trans-expr.c (gfc_apply_interface_mapping_to_expr): Do not
	dereference NULL pointer.


2018-03-02  Harald Anlauf  <anlauf@gmx.de>

	PR fortran/71085
	* gfortran.dg/pr71085.f90: New test.