coverity 158145 lws_header_table_detatch must handle no ah attached
coverity 158145 lws_header_table_detatch must handle no ah attached

callers should protect it so this doesn't make a problem.  But
Coverity is correct the code is confused about it.

Make it okay if we close a connection before the ah got attached.

Signed-off-by: Andy Green <b471f5a494de34531c9e5a6e15abda71edd49104@linaro.org>
sartura/libwebsockets,sartura/libwebsockets,ralight/libwebsockets,ralight/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,ralight/libwebsockets,ralight/libwebsockets,ralight/libwebsockets,sartura/libwebsockets,sartura/libwebsockets