[trunk] applied patch for null-reference bug in tilelayer/filecache, thanks Lunnez
[trunk] applied patch for null-reference bug in tilelayer/filecache, thanks Lunnez


git-tfs-id: [https://tfs.codeplex.com/tfs/TFS01]$/SharpMap/Trunk;C94326

SharpMap/SharpMap,nhvu1988/SharpMap,nhvu1988/SharpMap,SharpMap/SharpMap