Fix a minor bug with the column resize handle

If you override the CSS white-space property to 'normal', so that text
in the column headers can wrap, and you also enable manual column
resizing, the resize handle does not take up the full height of the
header.

This is a one-line fix for that problem.

(Note: I made the fix in the original src dir, but did not commit the
changes to the generated files. I assume you do that as part of a
build/distribution process. and didn't want them cluttering up the
commit.)