Prior to this commit, when the title string was empty and the close
button disabled, an extra empty line showed at the top of the message
box. This commit prevents adding the title label unless it has content
or is needed as a spacer for the close button.
As a positive side effect, this also prevents the default "text" from
displaying when NULL is passed as the title.
Co-authored-by: Gabor Kiss-Vamosi <kisvegabor@gmail.com>
2cd5a90b7d
