fix warnings introduced by commits 10139 and 10140

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@10142 b7f1a160-662a-0410-a6d8-bea165342f16
FIX: SparseLDLSolver: bad function call with uncalled-for NULL arguments

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@10143 b7f1a160-662a-0410-a6d8-bea165342f16
fixed FindSofa.cmake

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@10144 b7f1a160-662a-0410-a6d8-bea165342f16