SLADE crashes when creating a TEXTURE1 lump through the "Add to TEXTURES" option

[possiblyamagicmage]

SLADE Version: (3.2.4) Operating System: Windows 10 64-bit

Issue Details: When you right-click on a texture and select "Add to TEXTURES", then "Doom (TEXTURE1 + PNAMES)" and there isn't a PNAMES/TEXTUREx file already defined, the entire editor crashes. Even adding an empty TEXTUREx lump and importing PNAMES from an original IWAD crashes the editor. The only workaround I've found for this is to copy the TEXTUREx and PNAMES lumps from an IWAD, remove everything from TEXTUREX, then add your own textures into TEXTUREX. This ONLY happens with WADs - PK3s are not affected, and presumably folders are not affected either. No stacktrace is generated, either. The WAD is left untouched, though, so it doesn't corrupt it or anything.

https://github.com/sirjuddington/SLADE/assets/82590438/9d9d7670-8ba3-44ab-a47f-90a38b1b2d22