Check combined nesting depth limit

Ensure block indent depth and flow level are checked together against
MAX_NESTING_LEVEL, not independently. This prevents exceeding the
intended limit with e.g. 1000 block indents + 1000 flow levels.
Mirrors the approach already used in parser.c.

Author: ingydotnet

src/scanner.c

@@ -1181,7 +1181,7 @@ yaml_parser_increase_flow_level(yaml_parser_t *parser)
         return 0;
     }
 
-    if (parser->flow_level >= MAX_NESTING_LEVEL) {
+    if (parser->flow_level + (int)(parser->indents.top - parser->indents.start) >= MAX_NESTING_LEVEL) {
         return yaml_parser_set_scanner_error(parser,
                 "while increasing flow level", parser->mark,
                 "exceeded maximum nesting depth");
@@ -1235,7 +1235,7 @@ yaml_parser_roll_indent(yaml_parser_t *parser, ptrdiff_t column,
         if (!PUSH(parser, parser->indents, parser->indent))
             return 0;
 
-        if (!STACK_LIMIT(parser, parser->indents, MAX_NESTING_LEVEL)) {
+        if (!STACK_LIMIT(parser, parser->indents, MAX_NESTING_LEVEL - parser->flow_level)) {
             return yaml_parser_set_scanner_error(parser,
                     "while increasing block level", parser->mark,
                     "exceeded maximum nesting depth");