Fix bug : negative amount on debit/credit (GridAccount)

Fix bug : bad computation of next year due to previous commit

src/view/grid/GridAccount.cpp

@@ -722,6 +722,8 @@ void GridAccount::OnOperationModified(wxGridEvent& event)
 	pEditor->DecRef();
     }
 
+    if (new_op.amount < 0) new_op.amount *= -1;
+
     value = GetCellValue(row, CATEGORY);
     if (value.Length())
     {