Bug in NullCartesian fixed (it arose when I changed the name  of the extruder count in the preferences file to  NumberOfExtruders).
Bug in NullCartesian fixed (it arose when I changed the name 
of the extruder count in the preferences file to 
NumberOfExtruders).

git-svn-id: d2924805b4ae8fffc34e1a97dde5dc7532b2300d@668 cb376a5e-1013-0410-a455-b6b1f9ac8223

alx/reprap-host-software,alx/reprap-host-software