Fix spice errors when rerunning a simulation with measurements

Mark the simulation as not finished before starting it, preventing measurements from being requested
from spice right before simulation starts

(cherry picked from commit a5b7c65d)

eeschema/sim/simulator_frame.cpp

@@ -457,6 +457,8 @@ void SIMULATOR_FRAME::StartSimulation()
 
     if( simulatorLock.owns_lock() )
     {
+        m_simFinished = false;
+
         m_ui->OnSimUpdate();
         m_simulator->Run();