Merge pull request #703 from cesarBLG/default-signal-function

Add default signal function in case of SIGCFG errors

Author: cesarBLG

Source/Orts.Simulation/Simulation/Signalling/SignalHead.cs

@@ -50,7 +50,7 @@ public class SignalHead
         public float? ApproachControlLimitPositionM;
         public float? ApproachControlLimitSpeedMpS;
 
-        public SignalFunction Function { get; protected set; }
+        public SignalFunction Function { get; protected set; } = SignalFunction.UNKNOWN;
 
         public int ORTSNormalSubtypeIndex;     // subtype index form sigcfg file