Fixed WPILib restart bug by adding WPILib PID.

Change-Id: Ie51e7911e43f3b8b8055784097d2baba2e0eef1e
diff --git a/frc971/wpilib/wpilib_interface.cc b/frc971/wpilib/wpilib_interface.cc
index d7c23ce..5315b08 100644
--- a/frc971/wpilib/wpilib_interface.cc
+++ b/frc971/wpilib/wpilib_interface.cc
@@ -235,6 +235,7 @@
     {
       auto new_state = ::aos::robot_state.MakeMessage();
 
+      new_state->reader_pid = my_pid_;
       new_state->outputs_enabled = ds_->IsSysActive();
       new_state->browned_out = ds_->IsSysBrownedOut();