use 0xFFFD for INVALID_CHAR ("U+FFFD REPLACEMENT CHARACTER") instead of 0xFFFF

stepmania/src/FontCharAliases.cpp

@@ -68,7 +68,7 @@ static void InitCharAliases()
 		return;
 
 	CharAliases["default"]		= Font::DEFAULT_GLYPH;	/* ? */
-	CharAliases["invalid"]		= INVALID_CHAR;			/* 0xFFFF */
+	CharAliases["invalid"]		= INVALID_CHAR;			/* 0xFFFD */
 
 	/* The comments here are UTF-8; they won't show up in VC6 (use your
 	 * imagination). */

stepmania/src/RageUtil.cpp

@@ -953,7 +953,7 @@ bool utf8_is_valid( const CString &s )
 	return true;
 }
 
-const wchar_t INVALID_CHAR = 0xFFFF;
+const wchar_t INVALID_CHAR = 0xFFFD; /* U+FFFD REPLACEMENT CHARACTER */
 
 wstring CStringToWstring( const CString &s )
 {