Fix a memory leak in the processing of nested row values. This problem has

existed every since row values support was added (version 3.15.0, 2016-10-14)
but was only just now detected by OSSFuzz.

FossilOrigin-Name: 2df6bbf1b8ca881c8a465d6624de66fde4c5975ccae6b2f2dda392b137f577de

test/rowvalue.test

@@ -540,4 +540,10 @@ do_execsql_test 19.36 {
   SELECT * FROM t1 WHERE (3,32)>=(a,b) ORDER BY a DESC;
 } {2 22 1 11}
 
+# 2018-02-18: Memory leak nexted row-value.  Detected by OSSFuzz.
+#
+do_catchsql_test 20.1 {
+  SELECT 1 WHERE (2,(2,0)) IS (2,(2,0));
+} {0 1}
+
 finish_test