Lmms: Equalizer: The visualizer takes up most of the processing time of the plugin, regardless of whether or not the plugin is open

[SecondFlight]

Tested on my current working branch (master from a week ago) with debugging symbols.

Steps to reproduce:
1) Add equalizers to the master channel until you see a significant cpu drop when you play a note.
2) Disable visualizers on all equalizers
3) Play a note, notice that the CPU is significantly lower.

With visualizers enabled:

Without visualizers enabled:

[PhysSong]

Currently EQ uses EqSpectrumView::paintEvent to enable/disable analyzing, but the event function won't be called if the window is closed.
I think it should use the visibility of EqControlsDialog. I will fix this.

[curlymorphic]

I will correct this now.

[SecondFlight]

Fixed via the PR above.