TMX import crash with 3.6

[elvisish]

Plugin version
TilED importer: 2.4
Godot 3.6 beta 3

Issue description
When importing TMX on 3.6, Godot crashes and starts leaking memory until the entire machine locks up. Seemed to happen worse if the TilED file was saved directly into the folder instead of being copied in.

Steps to reproduce

• Add a TMX file to 3.6
• Double-click to load New Inherited scene
• Watch Godot crash

Sample map or tileset
N/A