nghttp2_hd: Fail inflate immediately if ctx.bad is nonzero

Doing inflation after error produces invalid results, especially, if
it is in NGHTTP2_HD_STATE_READ_INDEX, the inflater->left could be 0,
which causes assertion error.  Add sanity assertion for index

lib/nghttp2_hd.c

@@ -1390,6 +1390,10 @@ ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_inflater *inflater,
   uint8_t *last = in + inlen;
   int rfin = 0;
 
+  if(inflater->ctx.bad) {
+    return NGHTTP2_ERR_HEADER_COMP;
+  }
+
   DEBUGF(fprintf(stderr, "nghtp2_hd_infalte_hd start state=%d\n",
                  inflater->state));
   hd_inflate_keep_free(inflater);
@@ -1487,6 +1491,7 @@ ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_inflater *inflater,
         }
       } else {
         inflater->index = inflater->left;
+        assert(inflater->index > 0);
         --inflater->index;
         inflater->ent_name = nghttp2_hd_table_get(&inflater->ctx,
                                                   inflater->index);