Reverts the change to the in- and output proxy that sets its internal data value to the default value for its current data type. This was not the right thing to do. Upon (much) closer inspection, it turns out that the original issue that change was meant to address was more subtle than it initially appeared, and led back to the default texture initialized by the renderer being unbacked by any actual image data. The fix was to make sure that it was - we're now using a GMod-style purple checker-board texture to signal that a texture asset is missing or unassigned (images/no_texture.jpg).