Map editor incorrectly removes backslashes from UDMF quoted strings

[devinacker]

SLADE Version: (3.2.1)
Operating System: Windows

Issue Details:
When loading a UDMF map into the editor, any backslashes in front of escaped characters such as line breaks or inner quotes will be removed from string values, resulting in potentially invalid syntax after saving the map.

Example:
Before: comment="test1\r\n\"test2\"\r\ntest3"
After: comment="test1rn"test2"rntest3"