setAmplitudeModulator doesn't work on looping synths with no ADSR envelope

Platform: macOS 13
SDK version: 2.5
(Running on Playdate Simulator)

Relatively minor bug here:

If I call pd->sound->synth->setAmplitudeModulator with a PDSynth that has a looping sample, it has no effect, unless I've already called at least one function for setting the PDSynth's ADSR envelope. (i.e. setAttackTime, setDecayTime, setSystainLevel, or setReleaseTime)

Luckily this is easily worked around by just calling one of those functions, even if it's setting the value to 0. (It took a bit of poking around my code to figure out what was going wrong, though!)