[libgfortran,patch] Zero-length strings messed up in library (PR33079)

[François-Xavier Coudert]

>>   static char zero_length_string;
>>   *dest = &zero_length_string;
> Indeed this would be a good option as we currently do not deallocate
> that variable if len == 0.

Committed the amended version as rev. 127584. Thanks to both of you
for reviewing this patch!

FX