When the MaxSnaps configuration option is set to 0 the following panic
occurs during installation:
```
[PANICKED] Test Panicked
In [It] at: /usr/lib64/go/1.24/src/runtime/panic.go:115 @ 07/01/25 10:04:57.47
runtime error: index out of range [0] with length 0
Full Stack Trace
github.com/rancher/elemental-toolkit/v2/pkg/snapshotter.(*LoopDevice).cleanOldSnapshots(0xc00025a300)
/home/frelon/src/elemental-toolkit/pkg/snapshotter/loopdevice.go:468 +0x3e7
github.com/rancher/elemental-toolkit/v2/pkg/snapshotter.(*LoopDevice).CloseTransaction(0xc00025a300, 0xc000234a00)
/home/frelon/src/elemental-toolkit/pkg/snapshotter/loopdevice.go:271 +0x11d5
github.com/rancher/elemental-toolkit/v2/pkg/snapshotter_test.init.func3.12()
/home/frelon/src/elemental-toolkit/pkg/snapshotter/loopdevice_test.go:204 +0x38e
```
This commit checks that we don't try to delete old snapshots in case
there are none.
Signed-off-by: Fredrik Lönnegren <fredrik.lonnegren@suse.com>
(cherry picked from commit d8450e01b9)
f29ac2690f