Fix failure to rip CD tracks with special characters in their title

Certain characters such as ? have a special meaning in URLs so they have
to be encoded when used in path component, but the AudioCdCollection
fails to do so and just embeds the raw track title into the URL. Thus it
is impossible to rip tracks that contain such characters in their title,
as the URL passed to the KIO subsystem is invalid.

BUG: 224437
FIXED-IN: 2.6
REVIEW: 103841