Free err_info on WTAP_ERR_DECOMPRESS.

Change-Id: I57fbb17baf43b0f1365fef72778ac0e65935456a
Reviewed-on: https://code.wireshark.org/review/4210
Reviewed-by: Guy Harris <guy@alum.mit.edu>
(cherry picked from commit 22a0d65a9a6691bcec24905baefeaba370f04043)
Reviewed-on: https://code.wireshark.org/review/4212