Fix a faulty assert() in the SELECT code generator and add a test case

to prevent regression.

FossilOrigin-Name: 1421c8ffba179d6aafa2643012f80a2738779117

src/select.c

@@ -2603,7 +2603,7 @@ static int generateOutputSubroutine(
     */
     case SRT_Set: {
       int r1;
-      assert( pIn->nSdst==1 );
+      assert( pIn->nSdst==1 || pParse->nErr>0 );
       pDest->affSdst = 
          sqlite3CompareAffinity(p->pEList->a[0].pExpr, pDest->affSdst);
       r1 = sqlite3GetTempReg(pParse);