HTTP/2: fix handling of connection errors.
HTTP/2: fix handling of connection errors.

Previously, nginx worker would crash because of a double free
if client disconnected or timed out before sending all headers.

Found with afl-fuzz.

Signed-off-by: Piotr Sikora <ba6f3a1a6d7e1ecae91b31e93969cc392fbd0fdd@google.com>

firebase/nginx,firebase/nginx,firebase/nginx,firebase/nginx