Fixed division by zero error.
bz19826: display failed external downloads
bz19827: Fixed animation code crash.

If we got to _do_iteration() and the item list had already been
destroyed, then we would get the traceback in the list.
Fixed crash when playing from a selection
bz19356: added some checks to see if our playbin was destroyed
bz19370: don't crash if movies directory is not present
bz19372: Check that we can read from the version table on DB load

I'm not sure if this makes a difference, but the traceback in the
ticket crashed on get_version().  I added a call to that in the
database load code.  It's not going to affect performance and it seems
good to fail early, rather than in the later code.
bz19369: handle get_drive() returning None.

I'm not sure why it happened, but on janet's machine get_drive()
returned none.  Added some defensive programming to handle that.
Revert "bz19372: Check that we can read from the version table on DB load"

This reverts commit 99278f30c97932fce22b6cfcaf10bfb4c4445990.

That commit doesn't work when we are creating a new database.  I don't
think we really need it in any case, so let's just revert.
Log a warning when get_drive() returns None.
bz19373: remove device tab on settings change