B2017-272: For enhanced, use correct section type when creating a new section when previous sections in source are not linked.

B2017-272:  added a null check

PROMS/VEPROMS.CSLA.Library/Format/PlantFormat.cs

@@ -540,6 +540,7 @@ namespace VEPROMS.CSLA.Library
 		}
 		public List<StepDataRetval> StepGetLevelTypes(bool alwaysAdd, StepData topType, ref int cursel, string curType, ItemInfo _CurItemInfo)
 		{
+            if (topType == null) return null;
 			List<StepDataRetval> sds = new List<StepDataRetval>();
 			int retval = -1;
 			int cntitm = 0;