Handle network topology error in add_connector_loss function
Handle network topology error in add_connector_loss function

Other functions used be build_network raises NetworkTopologyError when
a fiber is not properly connected but this handling was missing from
add_connector_loss.

Change-Id: Id08cd4a9bad15f755d364a31ff3d38993d034447
Signed-off-by: Jonas Mårtensson <9c18489050b439bcd0a9df0d47735ceb99443dbb@ri.se>

Telecominfraproject/gnpy