message: Fix potential crash when no events found in expression
diff: @@ -395,22 +395,25 @@ public:
  {
  TraceEvents::loc_type_t type;
  const std::vector< uint32_t > *plocs = trace_events->get_locs( name.c_str(), &type );
  + size_t size = plocs ? plocs->size() : 0;
  + // Add expression to our added rows list
  m_graph_rows_add.push_back( name );
  for ( size_t i = 0; i < m_graph_rows_list.size(); i++ )
  {
  + // Add this new filter expression before the first comm / tdop expression event we find
  if ( m_graph_rows_list[ i ].type == TraceEvents::LOC_TYPE_Tdopexpr ||
  m_graph_rows_list[ i ].type == TraceEvents::LOC_TYPE_Comm )
  {
  - size_t size = plocs ? plocs->size() : 0;
  +
  m_graph_rows_list.insert( m_graph_rows_list.begin() + i,
  { type, size, name, false } );
  return;
  }
  }
  - m_graph_rows_list.push_back( { type, plocs->size(), name, false } );
  + m_graph_rows_list.push_back( { type, size, name, false } );
  }
  public:
  