add an assert

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@970 57a11ea4-9604-0410-9ed3-97b8803252fd

src/engine/Transaction.c

@@ -530,10 +530,10 @@ xaccSplitRebalance (Split *split)
    }								\
 }
 
-
 void
 xaccTransBeginEdit (Transaction *trans)
 {
+   assert (trans);
    trans->open = 1;
    xaccOpenLog ();
 }