Add an alert for blocked undergrounds

[DeadMG]

TL;DR

When an underground pipe/belt is blocked because of lava/space/etc, display an alert, either locally or globally or both.

Why?

Currently it's easy to accidentally block your undergrounds. This can occur because the blueprint construction is only blocked if the actual tiles are blocked, but the undergrounds can break if tiles not actually pasted in the blueprint are blocked by lava. This effectively means the player can place blueprints that don't work. Additionally you can remove space platform tiles (or Foundation but this is way less likely) that accidentally block up an underground without realising it until way too late. Considering the possibility of accidents (I just placed a print that happened to have one very hard to see tile of lava between two undergrounds so it just didn't work) it would be nice if the game made it obvious when this happened.

[kpreid]

+1 I've broken my space platforms this way a couple times even after learning the rule. "Oh I can just trim off this unused platform... whoops my asteroid chunks aren't flowing."

[evandy]

How would this distinguish from an underground that was placed too wide, or just a solo underground without a partner? Is this specifically only if they are blocked by lava? I feel like the display tips, and inability to create an underground by dragging already do a pretty good job of guarding against this... or am I missing something?

[Nemoricus]

This would be nice to have. There's a couple of times where I missed that a particular tile was actually lava and blocking my underground belts, and on space platforms you can sometimes miss a gap in the platform.