Spectrum model exception during handover

Reported here, with example program to reproduce: https://groups.google.com/g/ns-3-users/c/NC4I_bE_CZM

Attached program confirmed to fail on ns-3-dev:

assert failed. cond="m_spectrumModel == x.m_spectrumModel", +11.101214285s 4 file=../src/spectrum/model/spectrum-value.cc, line=203
terminate called without an active exception

handover_error_example.cc

Edited by Tom Henderson