Reset LastVisualX on undo/redo

In cursor's Goto(), which is currently only used by undo and redo, we
restore remembered LastVisualX and LastWrappedVisualX values. But if
the window had been resized in the meantime, the LastWrappedVisualX
may not be valid anymore. So it may cause the cursor moving to
unexpected locations.

So for simplicity just reset these values on undo or redo, instead of
using remembered ones.

internal/buffer/cursor.go

@@ -67,8 +67,9 @@ func (c *Cursor) Buf() *Buffer {
 // Goto puts the cursor at the given cursor's location and gives
 // the current cursor its selection too
 func (c *Cursor) Goto(b Cursor) {
-	c.X, c.Y, c.LastVisualX, c.LastWrappedVisualX = b.X, b.Y, b.LastVisualX, b.LastWrappedVisualX
+	c.X, c.Y = b.X, b.Y
 	c.OrigSelection, c.CurSelection = b.OrigSelection, b.CurSelection
+	c.StoreVisualX()
 }
 
 // GotoLoc puts the cursor at the given cursor's location and gives