Hotfix for tileset saving crash

New tiles were being created with their Name property set to null, which
caused null reference errors during the tileset saving process and
ultimately corrupted the tileset.
Hotfix for tileset saving crash

New tiles were created with Name set to null, which caused null
reference errors during tileset saving, corrupting the tileset in the
process.
Merge pull request #19 from fatcerberus/master

Fix tileset saving crash/corruption