libdwfl: Fix double free on failure path in gzip.c.

GCC10 -fanalyzer found a double free when openstream failed. When
openstream fails __libdw_gunzip will call fail, which frees the
state->buffer. But openstream can call zlib_fail, which will also
call fail. Instead of calling zlib_fail, just return the error
that zlib_fail would have returned.

Signed-off-by: Mark Wielaard <mark@klomp.org>
2 files changed