Fortran: fix passing of optional dummies to bind(c) procedures [PR113866]

	PR fortran/113866

gcc/fortran/ChangeLog:

	* trans-expr.cc (gfc_conv_procedure_call): When passing an optional
	dummy argument to an optional dummy argument of a bind(c) procedure
	and the dummy argument is passed via a CFI descriptor, no special
	presence check and passing of a default NULL pointer is needed.

gcc/testsuite/ChangeLog:

	* gfortran.dg/bind_c_optional-2.f90: New test.