Issue title: TEdit randomly crashes, don't know why
 Issue body: [TEditLog.txt](https://github.com/TEdit/Terraria-Map-Editor/files/1865874/TEditLog.txt)

TL:DR Giving me "Index was out of range. Must be non-negative and less than the size of the collection." error
 Comments: 
 Comment 0: [GitMate.io](https://gitmate.io) thinks possibly related issues are https://github.com/TEdit/Terraria-Map-Editor/issues/896 (Crashing), https://github.com/TEdit/Terraria-Map-Editor/issues/209 (Crash), https://github.com/TEdit/Terraria-Map-Editor/issues/121 (Crash), https://github.com/TEdit/Terraria-Map-Editor/issues/120 (Crash), and https://github.com/TEdit/Terraria-Map-Editor/issues/543 (TEdit crashes).
{'source': 'GithubIssues', 'repo_name_with_owner': 'TEdit/Terraria-Map-Editor', 'issue_id': 310268553, 'repo_stars': 1174.0}