Prevent a crash when loading a group with no additions in SongManager::LoadSongDir

When reloading and only loading additions, ensure we do not delete/readd groups that were already loaded.

src/SongManager.cpp

@@ -436,10 +436,14 @@ void SongManager::LoadSongDir( RString sDir, LoadingWindow *ld, bool onlyAdditio
 		RString group_base_name= Basename(sGroupDirName);
 		Group* group = new Group(sDir, sGroupDirName);
 		
+		// We need to keep track of previously loaded groups so we don't delete them if we're only loading additions
+		bool groupAlreadyLoaded = false;
 		// Add the group to the group mapping
 		if (m_mapNameToGroup.find(sGroupDirName) == m_mapNameToGroup.end())
 		{
 			m_mapNameToGroup[sGroupDirName] = group;
+		} else {
+			groupAlreadyLoaded = true;
 		}
 
 		for( unsigned j=0; j< arraySongDirs.size(); ++j )	// for each song dir
@@ -485,24 +489,28 @@ void SongManager::LoadSongDir( RString sDir, LoadingWindow *ld, bool onlyAdditio
 
 		LOG->Trace("Loaded %i songs from \"%s\"", loaded, (sDir+sGroupDirName).c_str() );
 
-		// Don't add the group name if we didn't load any songs in this group.
+		// If we're only loading additions, already loaded groups should neither be added nor deleted
-		if(!loaded) {
+		if (!(groupAlreadyLoaded && onlyAdditions)) {
-			// Remove the group from the group mapping
+
-			auto it = m_mapNameToGroup.find(sGroupDirName);
+			// Don't add the group name if we didn't load any songs in this group.
-			if (it != m_mapNameToGroup.end())
+			if(!loaded) {
-			{
+				// Remove the group from the group mapping
-				m_mapNameToGroup.erase(it);
+				auto it = m_mapNameToGroup.find(sGroupDirName);
+				if (it != m_mapNameToGroup.end())
+				{
+					m_mapNameToGroup.erase(it);
+				}
+				delete group;
+				continue;
 			}
-			delete group;
+
-			continue;
+			// Add this group to the group array.
+			AddGroup(sDir, sGroupDirName, group);
+
+			// Cache and load the group banner. (and background if it has one -aj)
+			IMAGECACHE->CacheImage( "Banner", GetSongGroupBannerPath(sGroupDirName) );
 		}
 
-		// Add this group to the group array.
-		AddGroup(sDir, sGroupDirName, group);
-
-		// Cache and load the group banner. (and background if it has one -aj)
-		IMAGECACHE->CacheImage( "Banner", GetSongGroupBannerPath(sGroupDirName) );
-
 		// Load the group sym links (if any)
 		LoadGroupSymLinks(sDir, sGroupDirName);
 	}
@@ -593,7 +601,7 @@ void SongManager::FreeSongs()
 	{
 		RageUtil::SafeDelete( song );
 	}
-    // Loop through all groups in the mapand delete them.
+    // Loop through all groups in the map and delete them.
 	for (auto it = m_mapNameToGroup.begin(); it != m_mapNameToGroup.end(); ++it)
 	{
 		Group* group = it->second;