instrument: a deck group's reserved cell width goes to the cells present

A Trigger face dropping Sustain and Release now gets wider cells instead of
144 px of dead slots. Group widths, row packing and Gate are untouched.

src/shell/instrument/editor_paint_deck.cpp

@@ -186,7 +186,6 @@ void ReaSamplerEditor::paintDeck(LICE_IBitmap* bmp, const FaceLayout& fl) {
         // The knobs. A dependent group's knobs draw Disabled (not hidden) — stable geometry.
         // The predicate is the input side's, so the drawn state and the inert grab agree.
         for (const DeckCellLayout& c : g.cells) {
-            if (c.id < 0) continue;  // reserved blank cell (the Trigger face's spare)
             const bool disabled = deckKnobDisabled(c.id);
             // A VELOCITY cell is a popup opener, not a dial: it shows its curve in miniature
             // where a knob face would be, and its whole cell is the click target.