fix: Skip processing transaction batch if the batch is empty (#5670)

Avoids an assertion failure in NetworkOPsImp::apply in the unlikely event that all incoming transactions are invalid.

src/test/app/NetworkOPs_test.cpp

@@ -0,0 +1,80 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2020 Dev Null Productions
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <test/jtx.h>
+#include <test/jtx/CaptureLogs.h>
+#include <test/jtx/Env.h>
+
+#include <xrpld/app/misc/HashRouter.h>
+
+namespace ripple {
+namespace test {
+
+class NetworkOPs_test : public beast::unit_test::suite
+{
+public:
+    void
+    run() override
+    {
+        testAllBadHeldTransactions();
+    }
+
+    void
+    testAllBadHeldTransactions()
+    {
+        // All trasactions are already marked as SF_BAD, and we should be able
+        // to handle the case properly without an assertion failure
+        testcase("No valid transactions in batch");
+
+        std::string logs;
+
+        {
+            using namespace jtx;
+            auto const alice = Account{"alice"};
+            Env env{
+                *this,
+                envconfig(),
+                std::make_unique<CaptureLogs>(&logs),
+                beast::severities::kAll};
+            env.memoize(env.master);
+            env.memoize(alice);
+
+            auto const jtx = env.jt(ticket::create(alice, 1), seq(1), fee(10));
+
+            auto transacionId = jtx.stx->getTransactionID();
+            env.app().getHashRouter().setFlags(
+                transacionId, HashRouterFlags::HELD);
+
+            env(jtx, json(jss::Sequence, 1), ter(terNO_ACCOUNT));
+
+            env.app().getHashRouter().setFlags(
+                transacionId, HashRouterFlags::BAD);
+
+            env.close();
+        }
+
+        BEAST_EXPECT(
+            logs.find("No transaction to process!") != std::string::npos);
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(NetworkOPs, app, ripple);
+
+}  // namespace test
+}  // namespace ripple