P_DoAllPlayersExit: Play finish sounds on successful execution

- If a local player is already finished, don't play any sound
- If the local players finish as a result of this, play the race finish line cross sound
- Else, play the race opponent finish line cross sound

src/p_user.c

@@ -1376,6 +1376,7 @@ void P_DoAllPlayersExit(pflags_t flags, boolean trygivelife)
 {
 	UINT8 i;
 	boolean givenlife = false;
+	const boolean dofinishsound = (musiccountdown == 0);
 
 	for (i = 0; i < MAXPLAYERS; i++)
 	{
@@ -1399,6 +1400,22 @@ void P_DoAllPlayersExit(pflags_t flags, boolean trygivelife)
 		givenlife = true;
 	}
 
+	if (!dofinishsound)
+	{
+		// You've already finished, don't play again
+		;
+	}
+	else if (musiccountdown == 0)
+	{
+		// Other people finish
+		S_StartSound(NULL, sfx_s253);
+	}
+	else if (musiccountdown > 1)
+	{
+		// Everyone finish sound
+		S_StartSound(NULL, sfx_s3k6a);
+	}
+
 	if (givenlife)
 	{
 		// Life sound