fix potential segfault (found by DerSaidin in xreal)

code/game/g_combat.c

@@ -974,7 +974,8 @@ void G_Damage( gentity_t *targ, gentity_t *inflictor, gentity_t *attacker,
 	}
 
 	// add to the attacker's hit counter (if the target isn't a general entity like a prox mine)
-	if ( attacker->client && targ != attacker && targ->health > 0
+	if ( attacker->client && client
+			&& targ != attacker && targ->health > 0
 			&& targ->s.eType != ET_MISSILE
 			&& targ->s.eType != ET_GENERAL) {
 		if ( OnSameTeam( targ, attacker ) ) {