Bug in parallel exitWith branch if a branch return undefined

[cl4cnam]

The bug appears when the branch returning undefined finished first.
For example:

parallel exitWith branch 1 ||
	awaitClickBeep('body')
||
	js ():
		return

gives the error message:

multiple value for cancellor variable --IN--  "... {foreach @all __par
		.var result
		:set result $__par
		{if [.get __par_N = 0]
			[ num   set   $result ]
		else
			:set retValMul $result
			{if [.get __par_N = $num]
				:breakReturn all $retValMul
			}
		}
	}

which is not informative.