Fix NULL pointer dereference in doloop_contained_function_call.

gcc/fortran/ChangeLog:

	PR fortran/96556
	* frontend-passes.c (doloop_contained_function_call):
	Do not dereference a NULL pointer for value.function.esym.

gcc/testsuite/ChangeLog:

	PR fortran/96556
	* gfortran.dg/do_check_15.f90: New test.