rtmpproto: Avoid rare crashes in the fail: codepath in rtmp_open

rtmpproto: Avoid rare crashes in the fail: codepath in rtmp_open

When running the cleanup in rtmp_close on failures in rtmp_open,
we can in rare cases end up using rt->playpath, assuming that it
is still set.

The crash could happen if we hit the fail codepath in rtmp_open
while publishing (rt->is_input == 0) with rt->state set to
a value > STATE_FCPUBLISH.

This would normally not happen while publishing; either we have
an error (and rt->state <= STATE_FCPUBLISH) or we reach
rt->state = STATE_PUBLISHING, and then we also return successfully
from rtmp_open.

The unexpected combination of states could happen if the server
responds with e.g. "NetStream.Play.Stop" while expecting
"NetStream.Publish.Start"; this sets rt->state to STATE_STOPPED,
which also fulfills the condition "> STATE_FCPUBLISH".

We don't need to free the rt->playpath/tcurl/flashver strings here;
they're handled via AVOption, and thus are freed automatically when
the protocol instance is freed (that's why they aren't freed
manually within the rtmp_close function either).

We also don't need to free the AVDictionary with options; it's
owned by the caller.

A smaller fix would be to just call rtmp_close before freeing
the strings and dictionary, but as we don't need to free them
at all, let's remove that redundant code.

Signed-off-by: Martin Storsj? <martin@martin.st>
(cherry picked from commit 8f4819ce01584e0858fdc312aa8a17c55e350a92)