i#2814: fix drreg double-restore (#2830)
i#2814: fix drreg double-restore (#2830)

After restoring a no-longer-reserved register, drreg now marks it native
and gives up its slot, avoiding an extra lazy restore later.

Fixes #2814
AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio