Fortran: fix simplification of TRANSFER for zero-sized character array result

Fortran: fix simplification of TRANSFER for zero-sized character array result

gcc/fortran/ChangeLog:

	PR fortran/104127
	* simplify.c (gfc_simplify_transfer): Ensure that the result
	typespec is set up for TRANSFER with MOLD of type CHARACTER
	including character length even if the result is a zero-sized
	array.

gcc/testsuite/ChangeLog:

	PR fortran/104127
	* gfortran.dg/transfer_simplify_11.f90: Fix logic.
	* gfortran.dg/transfer_simplify_13.f90: New test.

(cherry picked from commit 6c1a93102b41a558f3ad49a7c66015257535c747)