Fixed migration errors in v0.9.32

platform:  # supported: 2.0.4, 2.1.5, 2.2.0
backlogs:  # supported: 0.9.32
ruby:  # supported: 1.9.3, 1.8.7

I had to change execute to select_all and use explicit fields enumeration in the SELECT as otherwise connection returns an array of Mysql2::Result instead of array of hashes.
Also, fixed a 'nil-dereference'