Fortran: Fix READ with padding in BLANK ZERO mode.

	PR fortran/117819

libgfortran/ChangeLog:

	* io/read.c (read_decimal): If the read value is short of the
	specified width and pad mode is PAD yes, check for BLANK ZERO
	and adjust the value accordingly.
	(read_decimal_unsigned): Likewise.
	(read_radix): Likewise.

gcc/testsuite/ChangeLog:

	* gfortran.dg/pr117819.f90: New test.