levels: Fix secret lift in DM23.

The linedef triggering the secret lift mistakenly had its sector tag
set to zero, which causes the game to crash in Vanilla.

This fixes #94.
levels: Add missing player 1 start to DM32.

DM32 had deathmatch starts but was missing a player 1 start thing,
making it unplayable in single player mode.

This fixes #93.