WEAPON_MP5: Add a precache for the modelevent shell ejection sound shader,

in case a game does not compile with w_glock.qc included.

src/shared/w_mp5.qc

@@ -61,6 +61,7 @@ w_mp5_precache(void)
 #else
 	precache_model("models/v_9mmar.mdl");
 	precache_model("models/p_9mmar.mdl");
+	Sound_Precache("modelevent_shell.land");
 #endif
 }