Glyphs should clean-up or prune phantom layers when copying glyphs from other fonts

I copied the glyph “verticallineabovecomb” from NotoSans-MM.glyphs over to my font by Cmd+C-ing the glyph in the glyph overview and Glyphs copied over a host of layers that don’t exist in my font. In my source file (see GitHub link) I count 11 layers, of which 8 are displayed in Glyphs.

Edit: I jsut found that most of the spacing “glyphs” also have weird empty name layers. ufoLib choked on them as well… not idea how they got there.

glyphsLib chokes on these. Glyphs should insert them as new layers and/or ask the user to assign them to the existing ones to prevent silent data corruption.