Fix Vaccinator charge sounds playing 2+ times/tick

Due to prediction, the PrimaryAttack() function runs multiple times every tick.
Every time the function runs on a tick where the player gains another charge, it will stack a copy of the sound that plays, which quickly becomes extremely loud. Commonly this will play 2 or 3, but in testing I've seen upwards of 7 or 8 playing at the same time.

src/game/shared/tf/tf_weapon_medigun.cpp

@@ -1357,7 +1357,7 @@ bool CWeaponMedigun::FindAndHealTargets( void )
 				}
 
 #ifdef CLIENT_DLL
-					if ( GetMedigunType() == MEDIGUN_RESIST )
+					if ( GetMedigunType() == MEDIGUN_RESIST && prediction->IsFirstTimePredicted() )
 					{
 						// Play a sound when we tick over to a new charge level
 						int nChargeLevel = int(floor(flNewLevel/flMinChargeAmount));