Fix ubsan applying zero offset to null pointer occurred in unit test

lib/nghttp2_frame.c

@@ -899,9 +899,25 @@ nghttp2_settings_entry *nghttp2_frame_iv_copy(const nghttp2_settings_entry *iv,
 }
 
 int nghttp2_nv_equal(const nghttp2_nv *a, const nghttp2_nv *b) {
-  return a->namelen == b->namelen && a->valuelen == b->valuelen &&
-         memcmp(a->name, b->name, a->namelen) == 0 &&
-         memcmp(a->value, b->value, a->valuelen) == 0;
+  if (a->namelen != b->namelen || a->valuelen != b->valuelen) {
+    return 0;
+  }
+
+  if (a->name == NULL || b->name == NULL) {
+    assert(a->namelen == 0);
+    assert(b->namelen == 0);
+  } else if (memcmp(a->name, b->name, a->namelen) != 0) {
+    return 0;
+  }
+
+  if (a->value == NULL || b->value == NULL) {
+    assert(a->valuelen == 0);
+    assert(b->valuelen == 0);
+  } else if (memcmp(a->value, b->value, a->valuelen) != 0) {
+    return 0;
+  }
+
+  return 1;
 }
 
 void nghttp2_nv_array_del(nghttp2_nv *nva, nghttp2_mem *mem) {

lib/nghttp2_session.c

@@ -5353,9 +5353,11 @@ static ssize_t inbound_frame_effective_readlen(nghttp2_inbound_frame *iframe,
   return (ssize_t)(readlen);
 }
 
+static const uint8_t sin[] = {0};
+
 ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in,
                                  size_t inlen) {
-  const uint8_t *first = in, *last = in + inlen;
+  const uint8_t *first, *last;
   nghttp2_inbound_frame *iframe = &session->iframe;
   size_t readlen;
   ssize_t padlen;
@@ -5366,6 +5368,14 @@ ssize_t nghttp2_session_mem_recv(nghttp2_session *session, const uint8_t *in,
   size_t pri_fieldlen;
   nghttp2_mem *mem;
 
+  if (in == NULL) {
+    assert(inlen == 0);
+    in = sin;
+  }
+
+  first = in;
+  last = in + inlen;
+
   DEBUGF("recv: connection recv_window_size=%d, local_window=%d\n",
          session->recv_window_size, session->local_window_size);