[Patch] Fix some minor annoyances with TagDialogs

[Jeff Mitchell]

Aneurin Price wrote:
> Currently when editing tracks on a per-track basis in the TagDialog, 
> clicking next at the beginning of the playlist doesn't advance the 
> track on the first click, and similarly with previous at the end of 
> the playlist. The same thing happens if you change the traversal 
> direction (eg. next, next, previous - you need to click previous again 
> before it will go back).
> This is because the track list is accessed using a Java-style 
> iterator. From Qt docs:
> "Unlike STL-style iterators, Java-style iterators point *between* 
> items rather than directly *at* items."
Nye--

If the issue is non-STL style iterators, would it be better to just 
change m_trackIterator from a QListIterator to a QList::iterator 
instead?  i.e. accessed from QList::begin/QList::const_begin etc.  Those 
are STL style.

--Jeff