getaddrinfo: Fix resource leak after strdup failure in gethosts [BZ #25425]

Filip Ochnik spotted that one of the error jumps in gethosts fails to
call __resolv_context_put to release the resolver context.

Fixes commit 352f4ff9 ("resolv:
Introduce struct resolv_context [BZ #21668]") and commit
964263bb ("getaddrinfo: Release
resolver context on error in gethosts [BZ #21885]").

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>