Effects refactoring minor fixes

[daschuer]

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[Be-ing]

Build failed:

 In file included from /home/runner/work/mixxx/mixxx/src/effects/backends/builtin/autopaneffect.cpp:1:
/home/runner/work/mixxx/mixxx/src/effects/backends/builtin/autopaneffect.h: In constructor ‘RampedSample::RampedSample()’:
Error: /home/runner/work/mixxx/mixxx/src/effects/backends/builtin/autopaneffect.h:24:32: error: expression list treated as compound expression in mem-initializer [-fpermissive]
   24 |               initialized(false) {
      |                                ^
Error: /home/runner/work/mixxx/mixxx/src/effects/backends/builtin/autopaneffect.h:23:28: error: left operand of comma operator has no effect [-Werror=unused-value]
   23 |               currentValue(0, 0),
      |                            ^