Fix 'drawableSubprocessor' not being set when not loading settings or explicitly selecting a subprocessor

[ethanbb]

Currently, the LFP viewer has a bug where the canvas's drawableSubprocessor field doesn't get set in the typical case of adding a new LFP viewer to a signal chain and not selecting a subprocessor from the ComboBox. The updateSubprocessorSelectorOptions method selects the default subprocessor to display in the ComboBox, but doesn't send a notification, which is a problem because the ComboBox listener is responsible for setting drawableSubprocessor. The end result is that the canvas does not refresh properly and the data does not get displayed.

This fixes the bug by making updateSubprocessorSelectorOptions send a notification, and getting rid of a resulting circular call to updateSettings which should never be necessary, given the contexts in which the containing function LfpDisplayNode::setSubprocessor is currently called. The other change just removes a call to updateSubprocessorSelectorOptions which seems to be redundant with line 88 in that file.

[jsiegle]

Thanks for sorting this out! I've been trying to track down the cause of this for a while.

[ethanbb]

No problem! Now just trying to figure out why TTL events sometimes aren't showing up...

[jsiegle]

What does your subprocessor configuration look like? @aacuevas created a source with reconfigurable subprocessor streams/sample rates that could be useful for testing.

[ethanbb]

Actually never mind, looks like my problem was that I had the event channel turned off in the LFP viewer settings...thanks for helping me take a step back, I was getting pretty frustrated!