Makes frontier modsuit helmet airtight (#3618)

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## About The Pull Request
fixes #3606
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## Why It's Good For The Game
Space helmet, space worthy, airtight, not internal worthy??
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## Changelog

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:cl:
fix: frontier modsuit helmet now airtight
/:cl:

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monkestation/code/modules/blueshift/clothing/kahraman.dm

@@ -135,7 +135,7 @@
 			HELMET_FLAGS= list(
 				UNSEALED_LAYER = null,
 				UNSEALED_CLOTHING = SNUG_FIT|THICKMATERIAL,
-				SEALED_CLOTHING = STOPSPRESSUREDAMAGE,
+				SEALED_CLOTHING = STOPSPRESSUREDAMAGE|HEADINTERNALS,
 				UNSEALED_INVISIBILITY = HIDEFACIALHAIR|HIDEMASK|HIDEEARS|HIDEEYES|HIDEFACE|HIDEHAIR|HIDESNOUT,
 				UNSEALED_COVER = HEADCOVERSMOUTH|HEADCOVERSEYES|PEPPERPROOF,
 			),