BUG/MAJOR: stick-table: don't process store-response rules for applets

BUG/MAJOR: stick-table: don't process store-response rules for applets

The commit bc7c207f74 ("BUG/MAJOR: stick-tables: do not try to index a
server name for applets") tried to catch applets case when we tried to index
the server name. However, there is still an issue. The applets are
unconditionally casted to servers and this bug exists since a while. it's
just luck if it doesn't crash.

Now, when store rules are processed, we skip the rule if the stream's target
is not a server or, of course, if it is a server but the "non-stick" option
is set. However, we still take care to release the sticky session.

This patch must be backported to all stable versions.