Initialize dominant_ac also for ac_wrong_modifier

[skittlesvampir]

I don't use cut_on_ac_change but I still use ac_wrong_modifier because it provides a pretty accurate weight.

Before, dominant_ac was only initialized when cut_on_ac_change was enabled. If it didn't it was incorrectly reported as 0: Block 0 audio_channels (6) is different from dominant audio_channels (0). Block 0 score: Before - 0.50 After - 2.50

(I hope it's clear what I mean)

My patch seems to work but I don't know the codebase well so there might be a better way to do this.