Fix PB Burst Oversight (#5669)

# About the pull request

This PR fixes an oversight that allowed PB burst fires to be fired
without restriction during the burst sequence.

# Explain why it's good for the game

The gun shouldn't have a huge firerate increase just because you click
quickly point blank.

# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl: Drathek
fix: Fixed an oversight with burst point blank firing
/:cl:

code/modules/projectiles/gun.dm

@@ -1344,7 +1344,7 @@ and you're good to go.
 	user.next_move = world.time //No click delay on PBs.
 
 	//Point blanking doesn't actually fire the projectile. Instead, it simulates firing the bullet proper.
-	if(!able_to_fire(user)) //If it's a valid PB aside from that you can't fire the gun, do nothing.
+	if(flags_gun_features & GUN_BURST_FIRING || !able_to_fire(user)) //If it's a valid PB aside from that you can't fire the gun, do nothing.
 		return TRUE
 
 	//The following relating to bursts was borrowed from Fire code.