Converting an expression so that it can be passed by reference could
result in a NULL pointer dereference.

2020-06-04  Steven G. Kargl  <kargl@gcc.gnu.org>
	    Harald Anlauf  <anlauf@gmx.de>

gcc/fortran/
	PR fortran/95500
	* trans-expr.c (gfc_conv_expr_reference): Do not dereference NULL
	pointer.

gcc/testsuite/
	PR fortran/95500
	* gfortran.dg/pr95500.f90: New test.

(cherry picked from commit 8c727bdf4acf28c8315b119a1c8f6d6af745c2af)