[colr] Add MIN_SIZE to Paint

src/hb-ot-color-colr-table.hh

diff --git a/src/hb-ot-color-colr-table.hh b/src/hb-ot-color-colr-table.hh
index 09d762f..f01d383 100644
--- a/src/hb-ot-color-colr-table.hh
+++ b/src/hb-ot-color-colr-table.hh
@@ -524,6 +524,7 @@
 };
 
 struct Paint;
+
 // Paint a non-COLR glyph, filled as indicated by paint.
 struct PaintGlyph
 {
@@ -1152,6 +1153,8 @@
   Variable<PaintSkewAroundCenter>		paintformat31;
   PaintComposite				paintformat32;
   } u;
+  public:
+  DEFINE_SIZE_MIN (2);
 };
 
 struct BaseGlyphPaintRecord