https://crrev.com/690041 added handling for out of bound indices in
PDFiumPage::GetTextRunInfo(), but failed to consider a valid situation
where all the text in a text run are whitespaces. In this case,
GetTextRunInfo() needs to report the number of characters processed.

Add a test case with just a whitespace to test this condition.

Also update hello-world.in to have a {{streamlen}} macro and regenerate
hello-world.pdf

Bug: 997747
Change-Id: Id9e074080b19e4c642cf75fa6b72c5eb969197a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1769842Reviewed-by: Ian Prest <iapres@microsoft.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690811}