add utf8_is_valid

stepmania/src/RageUtil.cpp

@@ -770,6 +770,21 @@ int utf8_get_char_len (const char *pp)
 	return -1;
 }
 
+bool utf8_is_valid(const CString &str)
+{
+	unsigned pos = 0;
+	while(pos < str.size())
+	{
+		int len = utf8_get_char_len(str.c_str() + pos);
+		if(len == -1)
+			return false;
+
+		pos += len;
+	}
+
+	return true;
+}
+
 wchar_t utf8_get_char (const char *p)
 {
   int len = utf8_get_char_len(p);

stepmania/src/RageUtil.h

@@ -164,6 +164,7 @@ CString WcharToUTF8( wchar_t c );
 wstring CStringToWstring(const CString &str);
 wchar_t utf8_get_char (const char *p);
 int utf8_get_char_len (const char *p);
+bool utf8_is_valid(const CString &str);
 
 // Splits a CString into an CStringArray according the Deliminator.
 void split(