debugui: bug fix: Focus didn't work

Author: hajimehoshi

context.go

@@ -19,7 +19,6 @@ type Context struct {
 	hover         WidgetID
 	focus         WidgetID
 	currentID     WidgetID
-	lastID        WidgetID
 	lastZIndex    int
 	keepFocus     bool
 	hoverRoot     *container
@@ -76,7 +75,6 @@ func (c *Context) begin() {
 	c.hoverRoot = c.nextHoverRoot
 	c.nextHoverRoot = nil
 	c.currentID = emptyWidgetID
-	c.lastID = emptyWidgetID
 }
 
 func (c *Context) end() error {

helpers.go

@@ -13,7 +13,7 @@ func (c *Context) bringToFront(cnt *container) {
 }
 
 func (c *Context) Focus() {
-	c.setFocus(c.lastID)
+	c.setFocus(c.currentID)
 }
 
 func (c *Context) setFocus(id WidgetID) {