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.