PCLVisualizer::updateText doesn't always update, sometimes adds instead

This may possibly be user error, but I wanted to make a note of it here anyway, in case others experience it.

If I use addText to create 2D text in a visualization, providing an id manually, updating it does not always remove the old text — even when I again provide that id.

It strikes me that this may be a mismanagement of defaults problem, since the id defaults to the text string, and my text string is changing every loop iteration or so.

This does not appear to happen on the first viewport. If I have more than one viewport, it happens on the second. I'll let you know later whether it happens on the third and fourth.

Start at PCLVisualizer::addText and PCLVisualizer::updateText, focusing on manually supplied IDs, changing text strings, and behavior across multiple viewports. Reproduce the issue with a second viewport and verify that updating an existing ID replaces the old text rather than adding another item.