fix max_glyphs count when text wasn't passed in constructor

[FoamyGuy]

Issue was originally raised here: https://forums.adafruit.com/viewtopic.php?f=60&t=166798

This change will always include +1 to the value it passes for max_size to the super class Group. The extra one accounts for the background tilegrid which was introduced recently to fix background color for custom fonts. This way it does not matter whether the user passes text or max_glyphs in the constructor, the behavior is the same both ways.

Crash with current version and fix with new version tested with this:

import board
import terminalio
from adafruit_display_text import label


text = "Hello"
text_area = label.Label(terminalio.FONT, max_glyphs=5)
text_area.x = 10
text_area.y = 10
text_area.text = text
board.DISPLAY.show(text_area)
while True:
    pass

[jepler]

Makes sense to me. Didn't actually test.