decoders: Rephrase condition-less .wait() calls (self documentation)

decoders: Rephrase condition-less .wait() calls (self documentation)

Telling .wait() to "skip one sample" slightly obfuscates the intent of
getting the next samples while no condition applies. Explicitly pass no
condition arguments instead, to better reflect the purpose. Coincidently
these .wait() calls will execute in slightly less expensive code paths
in the common code.