Fix: an existing index == None should return False

[SKalt]

While using migra, I got the following error: AttributeError: 'NoneType' object has no attribute 'name'. Using pdb, I determined that the error arose when a table with an index was compared to one without an index. This patch eliminated the error.

[SKalt]

looks like all the circleci tests are failing with

sudo apt-get install -y postgresql-client
# E: Failed to fetch http://deb.debian.org/debian/pool/main/d/distro-info-data/distro-info-data_0.41+deb10u2_all.deb  404  # Not Found [IP: 199.232.166.132 80]
# E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

[SKalt]

@djrobstep, requesting a review

[SKalt]

^ same problem