Reduce the number of calls to memset() in sqlite3DbMallocZero().

FossilOrigin-Name: cede2bf8e42ac140a8cc75a1d173083f543ba467
diff --git a/src/expr.c b/src/expr.c
index d8d36af..3be3bf5 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -461,8 +461,9 @@
       assert( iValue>=0 );
     }
   }
-  pNew = sqlite3DbMallocZero(db, sizeof(Expr)+nExtra);
+  pNew = sqlite3DbMallocRaw(db, sizeof(Expr)+nExtra);
   if( pNew ){
+    memset(pNew, 0, sizeof(Expr));
     pNew->op = (u8)op;
     pNew->iAgg = -1;
     if( pToken ){