Fortran: Fix handling of the X edit descriptor.

This patch is a partial fix of handling of X edit descriptors
when combined with certain T edit descriptors.

	PR libfortran/114618

libgfortran/ChangeLog:

	* io/transfer.c (formatted_transfer_scalar_write): Change name
	of vriable 'pos' to 'tab_pos' to improve clarity. Add new
	variable next_pos when calculating the maximum position.
	Update the calculation of pending spaces.

gcc/testsuite/ChangeLog:

	* gfortran.dg/pr114618.f90: New test.