Allow .[-1] in path expressions

src/execute.c

@@ -687,6 +687,14 @@ jv jq_next(jq_state *jq) {
         set_error(jq, jv_invalid_with_msg(msg));
         goto do_backtrack;
       }
+      // $array | .[-1]
+      if (jv_get_kind(k) == JV_KIND_NUMBER && jv_get_kind(t) == JV_KIND_ARRAY) {
+        int idx = jv_number_value(k);
+        if (idx < 0) {
+          jv_free(k);
+          k = jv_number(jv_array_length(jv_copy(t)) + idx);
+        }
+      }
       jv v = jv_get(t, jv_copy(k));
       if (jv_is_valid(v)) {
         path_append(jq, k, jv_copy(v));