Do not end the whole androidqf run on an encrypted backup.ab (#891)

from_ab() raises InvalidAndroidBackup instead of exiting when it runs as a
sub-command, which check-androidqf catches to skip the backup modules. The
two password branches still called sys.exit(1) unconditionally, and since
run_backup_cmd() runs inside finish(), that ended the parent run before the
intrusion-logs command and before the timeline, alerts, urls, info and run
manifest were stored — leaving an output directory that looks complete but
has no alerts.json.

Also drop "as backup.ab is malformed" from the skip warning: it covers a
missing or wrong password too.

tests/test_check_android_androidqf.py

@@ -155,7 +155,7 @@ class TestCheckAndroidqfCommand:
             result = runner.invoke(check_androidqf, [str(path)])
 
         assert result.exit_code == 0
-        assert "Skipping backup modules as backup.ab is malformed" in caplog.text
+        assert "Skipping backup modules: Invalid backup format" in caplog.text
         assert not any(
             record.levelname in {"CRITICAL", "FATAL"} for record in caplog.records
         )