detect/pcre: fix memory read error in detect

detect/pcre: fix memory read error in detect

Fix case where a HTTP modifier in PCRE statements in a rule that would not
set the http protocol, would lead to a HTTP condition being run against
a non-HTTP flow. This would lead to invalid memory access.

Fix by properly setting the alproto and SIG_FLAG_APPLAYER flag in the
signature, leading to the signature implicitly setting the protocol
so rejecting it for inspection when the flow has a different protocol.

Bug #2863