~rjarry/aerc#287: Crash when running :pipe -m less

When selected message from #286 I get this crash:

mitmanek:python311.SUSE_SLFO_Main () $ aerc

aerc has encountered a critical error and has terminated. Please help us fix
this by sending this log and the steps to reproduce the crash to:
~rjarry/aerc-devel@lists.sr.ht

Thank you

Version: 0.18.2 +notmuch-5.6.0 (go1.23.2 amd64 linux 2024-11-02)

This error was also written to: /tmp/aerc-crash-20241102-141312.log
panic: runtime error: invalid memory address or nil pointer dereference [recovered]
	panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x55e9153c5081]

goroutine 219 [running]:
git.sr.ht/~rjarry/aerc/lib/log.PanicHandler()
	git.sr.ht/~rjarry/aerc/lib/log/panic-logger.go:51 +0x6cf
panic({0x55e9155a74e0?, 0x55e915b0a190?})
	runtime/panic.go:785 +0x132
git.sr.ht/~rjarry/aerc/commands/msg.Pipe.Run.func5()
	git.sr.ht/~rjarry/aerc/commands/msg/pipe.go:214 +0x1e1
created by git.sr.ht/~rjarry/aerc/commands/msg.Pipe.Run in goroutine 1
	git.sr.ht/~rjarry/aerc/commands/msg/pipe.go:196 +0x9e5
mitmanek:python311.SUSE_SLFO_Main () $

Status: REPORTED
Submitter: ~mcepl
Assigned to: No-one
Submitted: 30 days ago
Updated: 30 days ago
Labels: No labels applied.

~mcepl 30 days ago*

aerc from the commit e319d329.

~konimarti 30 days ago

git.sr.ht/~rjarry/aerc/commands/msg.Pipe.Run.func5() git.sr.ht/~rjarry/aerc/commands/msg/pipe.go:214 +0x1e1

It seems that the message info contains a nil envelope.

Line 214 in pipe.go only checks for a nil message info but not for a nil envelope before accessing info.Envelope.Subject. A nil envelope can occur when the backend cannot read or parse the message.