CLEANUP: http: message parser must ignore HTTP_MSG_ERROR

The issue only happens when DEBUG_FULL is enabled, which causes
http_msg_analyzer() to complain if it's called twice with an invalid
message, for instance because of two consecutive ACLs using req_proto_http.

The code is commented out when DEBUG_FULL is disabled, so this is not a bug,
just an annoyance for the developer.
diff --git a/src/proto_http.c b/src/proto_http.c
index ae30047..22623c0 100644
--- a/src/proto_http.c
+++ b/src/proto_http.c
@@ -1569,6 +1569,11 @@
 		msg->sol = buf->data + msg->som;
 		msg->msg_state = HTTP_MSG_BODY;
 		return;
+
+	case HTTP_MSG_ERROR:
+		/* this may only happen if we call http_msg_analyser() twice with an error */
+		break;
+
 #ifdef DEBUG_FULL
 	default:
 		fprintf(stderr, "FIXME !!!! impossible state at %s:%d = %d\n", __FILE__, __LINE__, state);