[addons] fix TranslateSingleString to be more robust to badly formatted strings
[pvr] fixes GetDirectoryFromPath() - don't consider slashes as first character
URIUtils::RemoveExtension didn't account for slashes after an extension, so could chop everything after the period in paths like /some/path.foo/some/other/folders/
Merge pull request #3670 from jmarshallnz/find_fixes

Find fixes
Don't flicker infomanager strings.

Just use the old values unless we're really busy.
[transforms] cleanup the transform stack to eliminate unnecessary copies.
[transforms] extend the UI transform with the font scaling amounts
[subs] scale subs rendered with our UI stuff correctly when in windowed mode
Merge pull request #3626 from jmarshallnz/subs_ui_scaling

Fix subtitle scaling for text based subs during windowed video playback