MojoLPM: fix bug in TestCase::Run

Similarly to checking the size of actions, we need to check the size of
the sequences to make sure those are not empty. Otherwise, we end up
having a DIVINT on line 676.

Change-Id: I20c847a07e5b0760a0ee9cf7a895b6c9f1952997
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4738599
Commit-Queue: Paul Semel <paulsemel@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/main@{#1178309}

mojo/public/tools/fuzzers/mojolpm.h

@@ -633,7 +633,7 @@ template <typename ProtoTestcase,
 bool Testcase<ProtoTestcase, ProtoAction, kMaxActionCount, kMaxActionSize>::
     IsFinished() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
-  if (!proto_testcase_.actions_size()) {
+  if (!proto_testcase_.actions_size() || !proto_testcase_.sequences_size()) {
     return true;
   }