Drowning while in pain state makes the player disappear

Order of operations thing.

• P_PlayerThink starts.
• Player dies to drowning in P_CheckUnderwaterAndSpaceTimer
• P_KillMobj strips you of all properties a dead player shouldn't have, such as MF2_DONTDRAW (the fix for a similar bug elsewhere in the code)
• P_KillMobj initiates state change from S_PLAY_PAIN to S_PLAY_DROWN
• P_SetPlayerMobjState, when the current state is S_PLAY_PAIN, sets pw_flashing to flashingtics-1.
• pw_flashing means P_PlayerThink toggles MF2_DONTDRAW on further down the main function
• P_PlayerThink ends, and is not called again next tic due to using the death thinker, which means MF2_DONTDRAW is never removed

The fix either involves bailing from P_PlayerThinker if the player is killed during it, making sure not to set pw_flashing in P_SetPlayerMobjState if the player is dead, only doing the MF2_DONTDRAW toggle if the player is alive, or some combination of these.

added Bug label

mentioned in merge request !1667 (merged)

mentioned in commit 646844bf

closed with merge request !1667 (merged)