Fortran: Fix issue with using snprintf function.

The previous patch used snprintf to set the message
string. The message string is not a formatted string
and the snprintf will interpret '%' related characters
as format specifiers when there are no associated
output variables. A segfault ensues.

This change replaces snprintf with a fortran string copy
function and null terminates the message string.

	PR libfortran/105456

libgfortran/ChangeLog:

	* io/list_read.c (list_formatted_read_scalar): Use fstrcpy
	from libgfortran/runtime/string.c to replace snprintf.
	(nml_read_obj): Likewise.
	* io/transfer.c (unformatted_read): Likewise.
	(unformatted_write): Likewise.
	(formatted_transfer_scalar_read): Likewise.
	(formatted_transfer_scalar_write): Likewise.
	* io/write.c (list_formatted_write_scalar): Likewise.
	(nml_write_obj): Likewise.

gcc/testsuite/ChangeLog:

	* gfortran.dg/pr105456.f90: Revise using '%' characters
	in users error message.