Fix unitialized value spotted by scan-build.
34 while (simgrid::s4u::Engine::getClock() < deadline) {
# (1) Loop condition is true. Entering loop body
35 void* received;
# (2) 'received' declared without an initial value
36 if (comm == nullptr)
# (3) Taking false branch
37 comm = mailbox->get_async(&received);
38 if (comm->test()) {
# (4) Assuming the condition is true
# (5) Taking true branch
39 // Retrieve the data sent by the peer.
40 TrackerQuery* tq = static_cast<TrackerQuery*>(received);
# (6) Assigned value is garbage or undefined
