widget: ensure empty editor makes space for caret

Prior to this change an editor with no content and a zero minimum
constraint would return itself has having width zero. This
prevented users from being able to see the editor when they
moved focus to it, as it could not display its caret. This
simple change ensures that, at minimum, the editor returns
its dimensions to include the width of a caret.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

widget/editor_test.go

@@ -36,6 +36,26 @@ var english = system.Locale{
 	Direction: system.LTR,
 }
 
+// TestEditorZeroDimensions ensures that an empty editor still reserves
+// space for displaying its caret when the constraints allow for it.
+func TestEditorZeroDimensions(t *testing.T) {
+	gtx := layout.Context{
+		Ops: new(op.Ops),
+		Constraints: layout.Constraints{
+			Max: image.Pt(100, 100),
+		},
+		Locale: english,
+	}
+	cache := text.NewCache(gofont.Collection())
+	fontSize := unit.Px(10)
+	font := text.Font{}
+	e := new(Editor)
+	dims := e.Layout(gtx, cache, font, fontSize, nil)
+	if dims.Size.X < 1 || dims.Size.Y < 1 {
+		t.Errorf("expected empty editor to occupy enough space to display cursor, but returned dimensions %v", dims)
+	}
+}
+
 func TestEditorConfigurations(t *testing.T) {
 	gtx := layout.Context{
 		Ops:         new(op.Ops),