Convert an assert() back into a conditional.  The conditional was converted
into an assert() by check-in [6ae4ad6ebee4db88] (2009-05-28) because we were
unable to find a test case for it.  Yongheng's fuzzer just now
found that test case.

FossilOrigin-Name: 4d0b9109f7a5312d4e136395e08b11dad64d746bc106ad44d47675e5b1dcb4ef
diff --git a/src/expr.c b/src/expr.c
index a5f9a43..76ffea3 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -2292,7 +2292,7 @@
     testcase( (p->selFlags & (SF_Distinct|SF_Aggregate))==SF_Aggregate );
     return 0; /* No DISTINCT keyword and no aggregate functions */
   }
-  assert( p->pGroupBy==0 );              /* Has no GROUP BY clause */
+  if( p->pGroupBy ) return 0;            /* Has no GROUP BY clause */
   if( p->pLimit ) return 0;              /* Has no LIMIT clause */
   if( p->pWhere ) return 0;              /* Has no WHERE clause */
   pSrc = p->pSrc;