fix: don't pipe plugin output more than once at the time

[pieh]

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Summary

#5899 made output unpiping conditional, however we still are piping for every hook leading to duplicated logs like so:

onBuild called onBuild called onPostBuild called onPostBuild called onPostBuild called onSuccess called onSuccess called onSuccess called onSuccess called onEnd called onEnd called onEnd called onEnd called onEnd called 

with number of repetitions increasing by one with each hook.

This attempts to ensure we don't have multiple active pipes, by return early if process was piped before without being unpiped

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[pieh]

this delete case is not hit if we return early in line 82, which would prevent from re-piping again in that case