Changing input on a connection causes full white-out

[ryanjjung]

To reproduce:

• Build a component with two inputs (like an assembler)
• Build a component with an output
• Connect the output of the second component to one of the inputs on the first component
• Now you have a conveyance drawn
• Edit the same connection
• Change the input to a different input on the same component
• Nothing changes visually
• When you drag the canvas around, the entire thing breaks

Logs show:

DEBUG:root:Draws are locked; refusing to draw a frame right now

So it's probably an erroneous block call getting made.

[ryanjjung]

Fixed a handful of things related to this logic in #130