Fixed min.cells.group issue in FindConservedMarkers()

[hamelyz]

Problem

FindConservedMarkers throws an error on too few cells even when parameter min.cells.group is lower than number of cells.

Distinct but related PR: #5079

The current behavior of FindConservedMarkers is the following:
If a group has greater than number of min.cells.group but less than 3 (the default for min.cells.group in function FindMarkers()) you get an error from ValidateCellGroups within FindMarkers because it is less than the threshold.

This is because the parameter min.cells.group, when used in FindConservedMarkers, was not passed down to FindMarkers

The error is as follows:

Error in `map()`:
ℹ In index: 4.
Caused by error in `ValidateCellGroups()`:
! Cell group 1 has fewer than 3 cells
Backtrace:
  1. ... 
 11. Seurat::FindConservedMarkers(...)
 13. Seurat:::FindMarkers.Seurat(...)
 15. Seurat:::FindMarkers.StdAssay(...)
 17. Seurat:::FindMarkers.default(...)
 18. Seurat:::ValidateCellGroups(...)
 19. base::stop("Cell group 1 has fewer than ", min.cells.group, " cells")
 

Implementation

I added the parameter to min.cells.group the FindMarkers() function that is run within FindConservedMarkers() so that that setting is passed down