Make _pLvlChanging into a boolean.

_pLvlChanging is only ever used in boolean contexts.

Source/msg.cpp

@@ -2337,7 +2337,7 @@ DWORD On_PLAYER_JOINLEVEL(TCmd *pCmd, int pnum)
 	if (gbBufferMsgs == 1)
 		msg_send_packet(pnum, p, sizeof(*p));
 	else {
-		plr[pnum]._pLvlChanging = 0;
+		plr[pnum]._pLvlChanging = FALSE;
 		if (plr[pnum]._pName[0] && !plr[pnum].plractive) {
 			plr[pnum].plractive = TRUE;
 			gbActivePlayers++;

Source/multi.cpp

@@ -791,7 +791,7 @@ void SetupLocalCoords()
 	plr[myplr]._ptargx = x;
 	plr[myplr]._ptargy = y;
 	plr[myplr].plrlevel = currlevel;
-	plr[myplr]._pLvlChanging = 1;
+	plr[myplr]._pLvlChanging = TRUE;
 	plr[myplr].pLvlLoad = 0;
 	plr[myplr]._pmode = PM_NEWLVL;
 	plr[myplr].destAction = ACTION_NONE;

Source/player.cpp

@@ -635,7 +635,7 @@ void CreatePlayer(int pnum, char c)
 		plr[pnum]._pSLvlVisited[i] = 0;
 	}
 
-	plr[pnum]._pLvlChanging = 0;
+	plr[pnum]._pLvlChanging = FALSE;
 	plr[pnum].pTownWarps = 0;
 	plr[pnum].pLvlLoad = 0;
 	plr[pnum].pBattleNet = 0;
@@ -1962,7 +1962,7 @@ void InitLevelChange(int pnum)
 
 	ClrPlrPath(pnum);
 	plr[pnum].destAction = ACTION_NONE;
-	plr[pnum]._pLvlChanging = 1;
+	plr[pnum]._pLvlChanging = TRUE;
 
 	if (pnum == myplr) {
 		plr[pnum].pLvlLoad = 10;

structs.h

@@ -227,7 +227,7 @@ typedef struct PlayerStruct {
 	BOOLEAN _pBlockFlag;
 	BOOLEAN _pInvincible;
 	char _pLightRad;
-	unsigned char _pLvlChanging;
+	BOOLEAN _pLvlChanging;
 	char _pName[PLR_NAME_LEN];
 	// plr_class enum value.
 	// TODO: this could very well be `enum plr_class _pClass`