mutt -A '' generates a segmentation fault
## Steps to reproduce
Simply run this to generate a segfault:
```
mutt -A ''
```
## What is the current bug behavior?
Segmentation fault
## What is the expected correct behavior?
empty result
## Mutt version
$ mutt -v
Mutt 2.3.2 (2026-04-26)
Copyright (C) 1996-2026 Michael R. Elkins and others.
Mutt comes with ABSOLUTELY NO WARRANTY; for details type `mutt -vv'.
Mutt is free software, and you are welcome to redistribute it
under certain conditions; type `mutt -vv' for details.
issue