Icon not shown when an update is available to mintupdate

[ParticleMon]

This should instead be labeled BUG.

Is your feature request related to a problem? Please describe.
When "Only show a tray icon when updates are available or in case of errors" is enabled, the icon is not shown when mintupdate can be updated. In this state, notification of all updates are suppressed indefinitely unless one manually checks for updates (with apt or mintupdate/Update Manager).

Describe the solution you'd like
When "Only show a tray icon when updates are available or in case of errors" is enabled, show the icon when an update to mintupdate is available.

Moreover, the editor in me suggests revising instances like "Only show a tray icon when..." and "Only show notifications for..." to "Show a tray icon only when..." and "Show notifications only for...."