juniper verify crashes with AttributeError when host's current cloud has no active assignment #751

Scenario

Fresh QUADS 3.0.x installation:

1. Define hosts in the spare pool (e.g. cloud01), add interfaces (em1/em2) with switch_ip/switch_port on a Juniper switch.
2. Create an assignment/schedule for another cloud (e.g. cloud02).
3. Before the first move completes (host still in cloud01), run:
   quads --verify-switch-conf --host <hostname> --change

What happens

juniper.verify() resolves the host's current cloud and calls get_active_cloud_assignment("cloud01"), which returns None (no active assignment on the spare pool). For a fresh switch port (no VLAN membership yet), parsing show configuration vlans | display set | match <port>.0 raises IndexError, and the except block reaches the unguarded if not _assignment.vlan: (src/quads/plugins/builtin/switches/juniper.py, ~line 267):

AttributeError: 'NoneType' object has no attribute 'vlan'

The CLI exits with an error for every host, so on a new installation the very first --verify-switch-conf validation fails.

Expected behavior

Never crash. When there is no active assignment for the host's current cloud, warn/skip ("no active assignment for cloud X, cannot verify") and return False, or proceed with derived VLAN values and warnings.

Suggested fix

Guard the None assignment:

-                            if not _assignment.vlan:
+                            if _assignment and not _assignment.vlan:

Notes

• Scope: manual CLI path (--host, or --cloud of a cloud without an active assignment).
• The automated --validate-env path is not affected: by then the host is in the target cloud and an active assignment exists.
• Reproduced on quads 3.0.2 (development branch, build 20261012), juniper plugin enabled.