Check actual free disk space when games ask.

Windows only for the moment.

Core/FileSystems/MetaFileSystem.h

@@ -108,6 +108,7 @@ public:
 	virtual int  Ioctl(u32 handle, u32 cmd, u32 indataPtr, u32 inlen, u32 outdataPtr, u32 outlen, int &usec);
 	virtual int  DevType(u32 handle);
 	virtual int  Flags() { return 0; }
+	virtual u64  FreeSpace(const std::string &path) override;
 
 	// Convenience helper - returns < 0 on failure.
 	int ReadEntireFile(const std::string &filename, std::vector<u8> &data);