Fix VolumeDirectory

Fixes the regression from a225426 and clarifies a related comment.

Source/Core/Common/FileUtil.cpp

@@ -499,6 +499,7 @@ FSTEntry ScanDirectoryTree(const std::string &directory, bool recursive)
 					entry = ScanDirectoryTree(physical_name, true);
 				else
 					entry.size = 0;
+				parent_entry.size += entry.size;
 			}
 			else
 			{

Source/Core/Common/FileUtil.h

@@ -58,7 +58,7 @@ namespace File
 struct FSTEntry
 {
 	bool isDirectory;
-	u64 size;                 // File length or number of entries from children
+	u64 size;                 // File length, or for directories, recursive count of children
 	std::string physicalName; // Name on disk
 	std::string virtualName;  // Name in FST names table
 	std::vector<FSTEntry> children;