Crash bug fix.

I ran into this on opensim.
The value of 'bucket' passed to parse_lure_bucket was empty.

In general, we should check we HAVE eight tokens, and not
just keep incrementing the iterator without checking.
Stop viewer from flooding the server.

On a parcel with voice disabled, the viewer keeps requesting voice info
every two frames, cycling between states stateNoChannel and
stateRetrievingParcelVoiceInfo.

This commit fixes that: if voice is disabled on the parcel then mAreaVoiceDisabled
is set (because the url is empty) and we stop requesting voice info until the parcel changes again.

If voice is enabled while we are in the stateNoChannel then we drop
out of that because mNextAudioSession gets set (to stateJoiningSession).

If the viewer has voice disabled, then now it drops correctly
out of the stateNoChannel into stateDisabled.