Fix resume on multi-episode files if no resume point is set.

When playing an item that belongs to a file containing multiple episodes and
the default select action is set to "Resume", but no resume point is set, it
was playing from the start of the file as it didn't check if an episode
bookmark existed, thus picking the wrong episode if it's not the first one.

"Play or resume" is not affected as it follows a slightly different logic.
Wouldn't
```
if (tag->m_iBookmarkId > 0)
```
be cleaner?