Can't share page with specific users, or add them to Calendar events (thumbnailLink is undefined, leading to JS error)

Summary

Attempting to add certain users to Team Calendar Events or sharing items with these users will redirect you to their User Profile instead.
This bug occurs when a user's avatar has spaces in its filename. This happens because we attempt to construct a java.net.URI from the path to the user's avatar without percent-encoding first - the space character is not permitted in a URI.
Affected users have a grey avatar icon instead of their own uploaded avatar.

Environment

• Confluence 6.0.0-OD-2016.02.1-0006
• Team Calendar 5.3.10-D20151229T094001

Steps to reproduce:

1. Open the share dialog on a page, or a calendar event
2. Type an affected user's name in the autocomplete field
3. In the autocomplete results observe that the user's avatar is not present, but is a grey person outline instead
4. Clicking on the result to add it the share dialog navigates to the profile page instead (hence losing the content that was typed in the share dialog) and the console shows a JS error originating from Confluence.Templates.Share.Dialog.recipientUser - when pausing on the error you can see that $thumbnailLink is undefined

Workaround

Affected users will need to upload a new profile picture which does not have any spaces in the filename.