fix: nil pointer dereference panic in shellAction

[paralin]

The shellAction function was calling cmd.Flags() directly multiple times throughout the function instead of using the flags variable that was already captured at the beginning (line 72).

In certain execution paths, cmd.Flags() could return nil, causing a panic:
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x98 pc=0x...]

This fix changes three locations to consistently use the flags variable:

• Line 164: workDir flag access
• Line 200: shell flag access
• Line 211: preserve-env flag access

Additionally, adds a nil check for inst.Config before accessing it to prevent similar panics and provide clearer error messages when instances have configuration errors.

[paralin]

This was to fix the following error I get:

cjs@flame ~ % lima -v
limactl version 2.0.2

cjs@flame ~ % lima
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x2 addr=0x98 pc=0x104f42f28]

goroutine 1 [running]:
main.shellAction(0x14000532f08, {0x140005805c0, 0x1, 0x1})
        /private/tmp/lima-20251124-4851-jwxwv0/lima-2.0.2/cmd/limactl/shell.go:165 +0x6c8
github.com/spf13/cobra.(*Command).execute(0x14000532f08, {0x14000580590, 0x1, 0x1})
        /Users/brew/Library/Caches/Homebrew/go_mod_cache/pkg/mod/github.com/spf13/[email protected]/command.go:1015 +0x7d4
github.com/spf13/cobra.(*Command).ExecuteC(0x14000532308)
        /Users/brew/Library/Caches/Homebrew/go_mod_cache/pkg/mod/github.com/spf13/[email protected]/command.go:1148 +0x350
github.com/spf13/cobra.(*Command).Execute(...)
        /Users/brew/Library/Caches/Homebrew/go_mod_cache/pkg/mod/github.com/spf13/[email protected]/command.go:1071
main.main()
        /private/tmp/lima-20251124-4851-jwxwv0/lima-2.0.2/cmd/limactl/main.go:50 +0x7c

[paralin]

I have tested and confirmed this works now.

[paralin]

Ci fail seems like a flake:

   TEST| [INFO] Uninstalling lima
  TEST| [INFO] Installing the old Lima v0.15.1
  curl: (22) The requested URL returned error: 504