Fix handling of bank select - LSB instead of MSB

[nickdowell]

amsynth was incorrectly ignoring the MIDI bank select LSB (CC20) and treating the MSB (CC0) as the back number (as sent by vkeybd)

Verified fix using jack-keyboard.

Addresses issue raised in #35 (comment)

[codecov]

Codecov Report

Merging #190 (d101d99) into develop (a8e78a9) will increase coverage by 0.03%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop     #190      +/-   ##
===========================================
+ Coverage    34.19%   34.23%   +0.03%     
===========================================
  Files           53       53              
  Lines         3193     3190       -3     
===========================================
  Hits          1092     1092              
+ Misses        2101     2098       -3     

Impacted Files	Coverage Δ
src/MidiController.cpp	55.23% <0.00%> (+0.94%)	⬆️

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