Error when disconnecting lines with set bus actions

[Tezirg]

Environment

• Grid2op version: 1.1.1
• System: ubuntu20

Bug description

Setting a line extremity bus to -1 will cause IndexError

How to reproduce

Code snippet

import grid2op
import numpy as np
print (grid2op.__version__)
env = grid2op.make("rte_case14_realistic")
action = env.action_space({'set_bus': {'substations_id': [(2, [-1, 0, 0, 0])]}})
print (action)
obs, reward, done, info = env.step(action)

Current output

1.1.1
This action will:
	 - NOT change anything to the injections
	 - NOT perform any redispatching action
	 - NOT force any line status
	 - NOT switch any line status
	 - NOT switch anything in the topology
	 - Set the bus of the following element:
	 - disconnect line (extremity) 2 [on substation 2]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/tezirg/Code/Grid2Op.bdonnot/grid2op/Environment/BaseEnv.py", line 906, in step
    self._backend_action += self.env_modification
  File "/home/tezirg/Code/Grid2Op.bdonnot/grid2op/Action/_BackendAction.py", line 293, in __iadd__
    self.current_topo.set_status(self._status_or_before[disco_before_topo],
  File "/home/tezirg/Code/Grid2Op.bdonnot/grid2op/Action/_BackendAction.py", line 108, in set_status
    self.values[id_reco_or] = old_vect[id_reco_or]
IndexError: index 4 is out of bounds for axis 0 with size 1

Expected output

1.1.1
This action will:
	 - NOT change anything to the injections
	 - NOT perform any redispatching action
	 - NOT force any line status
	 - NOT switch any line status
	 - NOT switch anything in the topology
	 - Set the bus of the following element:
	 - disconnect line (extremity) 2 [on substation 2]
Line_ex[2] is disconnected without error.