HaikuDepot: Display the last copyright line instead of the first.

As Diver notes in #13006:
> I saw a few youtube videos with Haiku review where people were confused
> with package copyright year in HaikuDepot. They though this was when the
> package was last updated. HaikuDepot also only shows the very first line of
> copyright year, so if it's multiline (which is quite often) they see very
> old timestamps.

We should eventually display some sort of modified time as well as all
of the copyright lines, but at the very least, we can display the last line
instead of the first line, which usually is much newer than the first.

src/apps/haikudepot/model/PackageInfo.cpp

@@ -526,7 +526,7 @@ PackageInfo::PackageInfo(const BPackageInfo& info)
 	BString publisherName = info.Vendor();
 	const BStringList& rightsList = info.CopyrightList();
 	if (rightsList.CountStrings() > 0)
-		publisherName = rightsList.StringAt(0);
+		publisherName = rightsList.Last();
 	if (!publisherName.IsEmpty())
 		publisherName.Prepend("© ");