Use the width of the widest line (not the first line) for the max

Use the width of the widest line (not the first line) for the max
width of the tooltip.  Also, don't set a narrower width if the tooltip
control already has a wider one.  It will automatically adjust smaller
if needed based on the \n's in the text.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@40829 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775