Add lua docs for GetPreferredSortSongsBySectionName, update comment, remove duplicate code

Docs/Luadoc/Lua.xml

@@ -1871,6 +1871,7 @@
 			<Function name='SetPreferredSongs'/>
 			<Function name='ShortenGroupName'/>
 			<Function name='SongToPreferredSortSectionName'/>
+			<Function name='GetPreferredSortSongsBySectionName'/>
 			<Function name='WasLoadedFromAdditionalCourses'/>
 			<Function name='WasLoadedFromAdditionalSongs'/>
 		</Class>

Docs/Luadoc/LuaDocumentation.xml

@@ -5908,6 +5908,9 @@ local args = {
 	<Function name='SongToPreferredSortSectionName' return='string' arguments='Song s'>
 		Returns the preferred sort section name for the specified Song.
 	</Function>
+	<Function name='GetPreferredSortSongsBySectionName' return='{Song}' arguments='string sSectionName'>
+		Returns a table containing all songs in the specified preferred sort section.
+	</Function>
 	<Function name='WasLoadedFromAdditionalCourses' return='bool' arguments='Course c'>
 		[Deprecated] Always returns <code>false</code>.
 	</Function>

src/MusicWheel.cpp

@@ -1245,8 +1245,8 @@ void MusicWheel::ChangeMusic( int iDist )
 bool MusicWheel::ChangeSort( SortOrder new_so, bool allowSameSort )	// return true if change successful
 {
 	ASSERT( new_so < NUM_SortOrder );
-	// Ignore allowSameSort if we're using SORT_PREFERRED
-	// Each player has their own preferred songs which sorts the songs differently -crashcringle
+	// NOTE(crashcringle): Ignore allowSameSort if we're using SORT_PREFERRED.
+	// Each player has their own preferred songs which sorts the songs differently
 	if( GAMESTATE->m_SortOrder == new_so && (!allowSameSort && new_so != SORT_PREFERRED ))
 	{
 		return false;

src/SongManager.cpp

@@ -861,14 +861,7 @@ void SongManager::GetPreferredSortSongsBySectionName( const RString &sSectionNam
 std::vector<Song*> SongManager::GetPreferredSortSongsBySectionName( const RString &sSectionName ) const
 {
 	std::vector<Song*> AddTo;
-	for (PreferredSortSection const &v : m_vPreferredSongSort)
-	{
-		if (v.sName == sSectionName)
-		{
-			AddTo.insert( AddTo.end(), v.vpSongs.begin(), v.vpSongs.end() );
-			return AddTo;
-		}
-	}
+	GetPreferredSortSongsBySectionName(sSectionName, AddTo);
 	return AddTo;
 }