fix(tooltip) : issue #1780, prevent rendering if text is whitespaces

tooltip : issue #1780, prevent rendering if text is whitespace.

Tooltips show, even if text is white spaces. The content (whitespaces) isn't even displayed, which in my opinion is inconsistent behavior ;) . My fix proposal is checking if the text is empty (as it is already), and whitespace(s) to prevent the tooltip rendering.

Cure : test for empty / blank content.