Merge pull request #739 from rouault/avoid_unsigned_integer_overflow

json_escape_str(): avoid harmless unsigned integer overflow

json_object.c

@@ -180,8 +180,9 @@ static int json_escape_str(struct printbuf *pb, const char *str, size_t len, int
 {
 	size_t pos = 0, start_offset = 0;
 	unsigned char c;
-	while (len--)
+	while (len)
 	{
+		--len;
 		c = str[pos];
 		switch (c)
 		{