[json/unmarshal] Fix quoted strings.

core/encoding/json/parser.odin

@@ -354,6 +354,12 @@ unquote_string :: proc(token: Token, spec: Specification, allocator := context.a
 
 	b := bytes_make(len(s) + 2*utf8.UTF_MAX, 1, allocator) or_return
 	w := copy(b, s[0:i])
+
+	if len(b) == 0 && allocator.data == nil {
+		// `unmarshal_count_array` calls us with a nil allocator
+		return string(b[:w]), nil
+	}
+
 	loop: for i < len(s) {
 		c := s[i]
 		switch {