fix for TextBox when initialized with an empty text

[FoamyGuy]

Another fix for TextBox

This fixes an issue when TextBox is initialized with empty Text the self._bitmap can be None when it tries to fill it with background color. By ensuring that kwargs["text"] is set to a space instead of empty string before the call to super init it ensures that the Bitmap will always get created.

[FoamyGuy]

The latest commits avoid the text property of the TextBox containing a space after it was initialized as empty. In most cases this would not matter, but in my use case I am doing input_box.text += keyboard_keys so the extra space gets preserved during concatenation with incoming new text.

Also used _full_text internally within TextBox in a few more places which is more correct now after the refactoring, though in this case doesn't cause any difference in behavior.

[dhalbert]

This seems ok, but could self._bitmap always be created even if the text is empty? Then there is no hack needed.

[FoamyGuy]

I will merge this for now to resolve the exception.

I can also look into always creating the bitmap without resorting to spoofing the text value. I think I tried that way first and it caused some of the bounding box calculations from where the bitmap is created to turn out differently and made the box shift upwards some.
I'll try to get it working that way and make a follow up PR that swaps out the workaround for a better approach.