gdb/guile: Do not error when trying to create empty array.

gdb/guile: Do not error when trying to create empty array.

This fixes a similar error as in the Python support code where
trying to create an empty array.

In guile/scm-type.c::tyscm_array_1, the funtion raises an exception
if N2 < N1:

   if (n2 < n1)
     {
       gdbscm_out_of_range_error (func_name, SCM_ARG3,

But it should be doing so if N2 == N1 - 1, since that would simply
be an empty array, not an array with a negative length.

gdb/ChangeLog:

        * guile/scm-type.c (tyscm_array_1): Do not raise out-of-range
        error if N2 is equal to N1 - 1.