Incorrect FirstSubdivInfoNumber for first map level

[Hiller]

Hi.
First. Thanks for a nice library. Great job
Second. I found a bug in SimpleTileMap processing. During map levels creation FirstSubdivInfoNumber for first map level is set to 1. In GetFileData function there's a retrieval of MapLevel for Subdivision index which is 0 based

for (int i = 0; i < rgn.SubdivList.Count && i < tre.SubdivInfoList.Count; i++) {
            int level = SymbolicScaleDenominatorAndBitsLevel.Level4SubdivIdx1(i);

public int Level4SubdivIdx1(int idx) {
            for (int i = Count - 1; i >= 0; i--)
               if (idx >= FirstSubdivChildIdx(i))
                  return i+1;//first map level is always empty(covered by basemap)
            return Count - 1;
         }

In this case level for first supposed map level subdivision will be returned incoreclty