message: fix HIP Fbcsr SpMV
  It's still broken for strided accesses though
diff: @@ -133,7 +133,7 @@ void spmv(std::shared_ptr<const HipExecutor> exec,
  // empty output: nothing to do
  return;
  }
  - if (b->get_size()[0] == 0) {
  + if (b->get_size()[0] == 0 || a->get_num_stored_blocks() == 0) {
  // empty input: fill output with zero
  dense::fill(exec, c, zero<ValueType>());
  return;
  @@ -192,7 +192,7 @@ void advanced_spmv(std::shared_ptr<const HipExecutor> exec,
  // empty output: nothing to do
  return;
  }
  - if (b->get_size()[0] == 0) {
  + if (b->get_size()[0] == 0 || a->get_num_stored_blocks() == 0) {
  // empty input: scale output
  dense::scale(exec, beta, c);
  return;
  