Fix xaccSplitGetOtherSplit which was broken by 028bf9826, don't

count splits that aren't really in the transaction.

The rewrite left out one test.  This was most obvious in the dummy
transaction used to enter a new transaction into an account.
xaccSplitGetOtherSplit never returned an "other split" for this
transaction.  It turns out the old code was broken too, but
it worked for this case by coincidence.

libgnucash/engine/Split.c

@@ -2107,6 +2107,7 @@ xaccSplitGetOtherSplit (const Split *split)
     {
         Split *s = n->data;
         if ((s == split) ||
+            (!xaccTransStillHasSplit(trans, s)) ||
             (xaccAccountGetType (xaccSplitGetAccount (s)) == ACCT_TYPE_TRADING) ||
             (qof_instance_has_slot (QOF_INSTANCE (s), "lot-split")))
             continue;