Fixes pointblanks (#4261)

# About the pull request

These are very different when unnested.

Fixes #4260

# Explain why it's good for the game

Bug bad and I died because I couldn't PB :(


# 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: Morrow
fix: Fixed pointblanks
/:cl:

code/modules/projectiles/gun.dm

@@ -1343,10 +1343,11 @@ and you're good to go.
 
 	//The following relating to bursts was borrowed from Fire code.
 	var/check_for_attachment_fire = FALSE
-	if(active_attachable?.flags_attach_features & ATTACH_PROJECTILE)
-		check_for_attachment_fire = TRUE
-	else
-		active_attachable.activate_attachment(src, null, TRUE)//No way.
+	if(active_attachable)
+		if(active_attachable.flags_attach_features & ATTACH_PROJECTILE)
+			check_for_attachment_fire = TRUE
+		else
+			active_attachable.activate_attachment(src, null, TRUE)//No way.
 
 
 	var/bullets_to_fire = 1