Combine the xFunc and xStep pointers of the FuncDef object into a single
pointer xSFunc.

FossilOrigin-Name: 0d1b3d7d3ca66cb0b97493f1aeade1703af3c9f4
diff --git a/src/resolve.c b/src/resolve.c
index bb66462..97cb655 100644
--- a/src/resolve.c
+++ b/src/resolve.c
@@ -665,7 +665,7 @@
           wrong_num_args = 1;
         }
       }else{
-        is_agg = pDef->xFunc==0;
+        is_agg = pDef->xFinalize!=0;
         if( pDef->funcFlags & SQLITE_FUNC_UNLIKELY ){
           ExprSetProperty(pExpr, EP_Unlikely|EP_Skip);
           if( n==2 ){