Added checks to validate that the selection list is non-empty

Added protection for invalid / empty inventory contents

SH-4125 FIX - problem was unpredictable ordering of avatar and llviewerregion deletion. Avoid trying to send metrics when we're shutting down and it's too late anyway. Reviewed by Nyx

Added an additional sanity check to make sure that other avatars don't
affect your wearables.

Reverting fix as additional problems were found that could lead to even accidental nudity.
This fix is not required for the current release as it is not a regression.
Will review options for fixing for the next release.

Added a constraint to ensure that the avatar's height (with offset)
does not go below 0.1 meters. Camera was getting confused since the avatar's
effective height was negative.

Note the avatar is mostly underground/contorted even at 0.1 meters, but
most users setting values this low will be making ultra-tinies and would
be hiding the avatar mesh. Camera stays above ground when height is at 0.1.

SH-4057 FIX - host bake textures should start with UDP fetching now, instead of waiting to fail down