pan/mdg: Analyze helper termination after scheduling
Similar to the fix in 6bf8e960 ("pan/bi: Do helper termination analysis on clauses") Though apparently a "theoretical issue only", fixes artefacts in DarkPlaces with both D3D9 and GL renderers. Fixes: 9a7f0e26 ("pan/mdg: Use the helper invo analyze passes") Part-of: <!12156> (cherry picked from commit a2b37e95)