Mortran codes fail to run with -fbounds-check flag

[rtownson]

The mortran codes crash if they have been compiled with -fbounds-check. The error looks like this:

At line 17895 of file dosxyznrc_test.F
Fortran runtime error: Substring out of bounds: lower bound (-1) of 'filen' is less than one

Thanks to /u/pvoytas for reporting this: https://www.reddit.com/r/EGSnrc/comments/m0p1r9/usercode_fortran_runtime_errors_with_boundscheck/