Caused by rB4212b6528af.
outlineColor is computed by the vertex shader, so not a uniform.
So outlineColor was undefined.
note: it was still possible to run into the situation that a selected UV
is drawn ontop of a selected pinned UV [you had to disable sticky
selection for this], now also make sure selected-pinned are drawn
topmost, then selected, then unselected UVs.