Fix loading a newly created connectivity in Connectivity viewer

2020-09-10 12:38:41,222 - ERROR - tvb.interface.web.controllers.decorators - An unexpected exception appeared
Traceback (most recent call last):
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/interfaces/web/controllers/decorators.py", line 153, in deco
 return func(*a, **b)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/interfaces/web/controllers/decorators.py", line 81, in deco
 template_dict = func(*a, **b)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/interfaces/web/controllers/decorators.py", line 200, in deco
 return func(*a, **b)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/interfaces/web/controllers/decorators.py", line 272, in deco
 return func(*a, **b)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/interfaces/web/controllers/decorators.py", line 257, in deco
 return func(*a, **b)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/interfaces/web/controllers/flow_controller.py", line 225, in default
 template_specification = self.execute_post(project.id, submit_link, step_key, algorithm, **data)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/interfaces/web/controllers/autologging.py", line 1053, in autologging_traced_instancemethod_delegator
 return method(*args, **keywords)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/interfaces/web/controllers/flow_controller.py", line 311, in execute_post
 result = adapter_instance.launch(view_model)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/adapters/visualizers/connectivity.py", line 218, in launch
 view_model.step)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/adapters/visualizers/connectivity.py", line 386, in compute_parameters
 numpy.asarray(colors)[input_data.hemispheres], X_CANVAS_SMALL, Y_CANVAS_SMALL)
 File "/WORK/TVB_GIT/tvb-root/framework_tvb/tvb/adapters/visualizers/connectivity.py", line 423, in _get_json
 max_y = max(positions[:, coord_idx2])
ValueError: max() arg is an empty sequence