PerfMonComps: Don't leave the first event flag true when component-level monitoring is disabled in PerfMonMT

This one is mostly for completeness and to avoid confusion down the road. We're currently not toggling the isFirstEvent flag off when component-level measurements are disabled. Although in that mode this flag is not really used (hence the sloppiness), this MR toggles it off through the relevant incident instead to avoid possible confusion in the future.