Fix monsters being unable to see the player if he generates noise.

When searching for the player FinTarget() always goes after sound
targets and aborts as soon as it finds one. So if the player is
constantly generating sounds - for example firing the machine gun -
there's a high chance that monsters will only hear but never see
him. Work around this by adding a small timeout to player noises, make
sure that at least 3 frames passed since the last noise. This gives
monsters 2 frames to see the player.

This bug was present in the original code, this is a small gameplay
change.

The problem was analysed by @BjossiAlfreds in #436. He also suggested
the fix.

src/game/player/weapon.c

@@ -123,12 +123,22 @@ PlayerNoise(edict_t *who, vec3_t where, int type)
 
 	if ((type == PNOISE_SELF) || (type == PNOISE_WEAPON))
 	{
+		if (level.framenum <= (level.sound_entity_framenum + 3))
+		{
+			return;
+		}
+
 		noise = who->mynoise;
 		level.sound_entity = noise;
 		level.sound_entity_framenum = level.framenum;
 	}
 	else
 	{
+		if (level.framenum <= (level.sound2_entity_framenum + 3))
+		{
+			return;
+		}
+
 		noise = who->mynoise2;
 		level.sound2_entity = noise;
 		level.sound2_entity_framenum = level.framenum;