Fix NPE and include "bridge-distribution-request" lines in sanitized bridge descriptors
For NPE log excerpt see comment:1.
From CollecTor's logs:
2017-10-25 02:09:20,131 WARN o.t.c.b.SanitizedBridgesWriter:952 Unrecognized line 'bridge-distribution-request any'. Skipping.
We should investigate what the exact specification of this line is, decide whether it's harmless to keep, add it to CollecTor's bridge descriptor module, try it out locally, get it reviewed, put out a release, and deploy that.