Insert a sanity hack from Melchior that apparently prevents a NaN from

popping up and crashing when the B-29 model is in use.  This isn't the
right solution; we should fine the NaN condition.  But it's harmless
and allows development with the B-29 to continue.

src/FDM/YASim/PropEngine.cpp

@@ -176,6 +176,8 @@ void PropEngine::integrate(float dt)
     _eng->setFuelState(_fuel);
     
     _prop->calc(_rho, speed, _omega * _gearRatio, &thrust, &propTorque);
+    if(_omega == 0.0)
+        _omega = 0.001; // hack to get around reports of NaNs somewhere...
     propTorque *= _gearRatio;
     _eng->calc(_pressure, _temp, _omega);
     _eng->integrate(dt);