Infinite Flare bugfix! (#4293)

# About the pull request
Fixes a flare gun bug where you would be able to do some funky stuff
with unloading while doing the unique action, causing you to be able to
unload infinite flares from the flare gun.
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# Explain why it's good for the game
Bug bad
# Testing Photographs and Procedure
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<summary>Screenshots & Videos</summary>

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# Changelog
:cl:
fix: Fixes an infinite flare bug
/:cl:

code/modules/projectiles/guns/specialist.dm

@@ -1486,6 +1486,9 @@
 	if(!do_after(user, 1 SECONDS, INTERRUPT_ALL, BUSY_ICON_GENERIC))
 		return
 
+	if(!current_mag || !current_mag.current_rounds)
+		return
+
 	current_mag.current_rounds--
 
 	flare_turf.ceiling_debris()