hiding staves removes complete system

[Toine Schreurs]

>From an orchestral score I want to create a score of the percussion 
instruments only. Now percussionists are used to large numbers of rests.
\RemoveEmptyStaffContext is very usefull in leaving out staves with
no musical content.
But if all of the staves in one system only contain rests, the whole system
disappears. It would be nice to leave at least one staff visible.

Example:

  \version "2.7.28"

  \layout {
    \context { \RemoveEmptyStaffContext }
  }

  partA = \relative c' { 
    R1*10 \mark \default
    R1*10 \mark \default
    R1*10 \mark \default
    R1*10 \mark \default
    R1*10 \mark \default
    R1*10 \mark \default
    c4 r r2
   }

  partB = \relative c' { 
    R1*60
    d4 r r2
   }

  \score {
    \new StaffGroup <<
      \new Staff \partA 
      \new Staff \partB
    >>
  }

-- 
Toine Schreurs