collect: Properly report tasks collecting error
collect: Properly report tasks collecting error

When we've failed to seize tasks we should report this error to the caller.

Reported-by: Kevin Wilson <2c2af831d066b4ea6d09315d50db14f93646f4a9@gmail.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@parallels.com>

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