Make sure grpc_secure_channel_create() never returns NULL.

src/core/ext/transport/chttp2/client/secure/secure_channel_create.c

@@ -144,5 +144,8 @@ grpc_channel *grpc_secure_channel_create(grpc_channel_credentials *creds,
                                 "secure_client_channel_factory_create_channel");
   grpc_channel_args_destroy(&exec_ctx, new_args);
   grpc_exec_ctx_finish(&exec_ctx);
-  return channel; /* may be NULL */
+  return channel == NULL ? channel
+                         : grpc_lame_client_channel_create(
+                               target, GRPC_STATUS_INTERNAL,
+                               "Failed to create secure client channel");
 }

test/core/end2end/fuzzers/api_fuzzer.c

@@ -1155,6 +1155,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
           grpc_channel_args *args = read_args(&inp);
           grpc_channel_credentials *creds = read_channel_creds(&inp);
           g_channel = grpc_secure_channel_create(creds, target_uri, args, NULL);
+          GPR_ASSERT(g_channel != NULL);
           {
             grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
             grpc_channel_args_destroy(&exec_ctx, args);