brush widget UI: don't allow 0 width or height

src/metabrushes/MetaBrush/Brush/Widget.hs

@@ -122,13 +122,16 @@ widgetUpdate widget mode ( oldPt, newPt ) ( MkR oldFlds ) =
       | ℝ3 w h θ <- oldFlds
       -> case mode of
         ScaleAction whatScale ->
-          let T ( ℝ2 w' h' ) = rotate ( cos -θ ) ( sin -θ ) newPt
+          let T ( ℝ2 w0 h0 ) = rotate ( cos -θ ) ( sin -θ ) newPt
+              -- Don't allow width/height to become 0.
+              w' = max 1e-6 ( abs w0 )
+              h' = max 1e-6 ( abs h0 )
           in case whatScale of
-                ScaleXY -> MkR $ ℝ3 ( abs w' ) ( abs h' ) θ
+                ScaleXY -> MkR $ ℝ3 w' h' θ
-                ScaleX  -> MkR $ ℝ3 ( abs w' )       h    θ
+                ScaleX  -> MkR $ ℝ3 w' h  θ
-                ScaleY  -> MkR $ ℝ3       w    ( abs h' ) θ
+                ScaleY  -> MkR $ ℝ3 w  h' θ
         RotateAction {}
-          | norm newPt < 1e-5
+          | norm newPt < 1e-6
           -> MkR oldFlds
           | otherwise
           ->