libdw: Initialize filelist earlier in dwarf_getsrclines.c read_srclines.

libdw: Initialize filelist earlier in dwarf_getsrclines.c read_srclines.

I'm getting this error with 0.172:

dwarf_getsrclines.c: In function 'read_srclines':
dwarf_getsrclines.c:1074:7: error: 'filelist' may be used uninitialized in this function [-Werror=maybe-uninitialized]
       free (filelist);
       ^~~~~~~~~~~~~~~

It seems that gcc is right here as there is "ifs" that go to "out"
(where filelist is freed) before freelist is initialized.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>