Add a space after "View Inline" in mail to prevent double-click on the filename from selecting "Inline"

Summary:
See PHI920. Ref T13210. Since the HTML is just:

<a>View Inline</a><span>filename.txt</span>

..double-clicking "filename.txt" in email selects "Inlinefilename.txt".

Add a space to stop this. At least in Safari, a space between the tags is not sufficient (perhaps because the parent is a <div>?). I couldn't find an authoritative-seeming source on what the rules for this actually are and adding a space here fixes the issue without changing the visual rendering, so just put it here.

Test Plan:

• Made an inline.
• Used bin/mail show-outbound --id ... --dump-html to dump the HTML.
• Double-clicked the filename.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13210

Differential Revision: https://secure.phabricator.com/D19742