When generating data for a RETURNING clause, avoid assuming cursor number 0 is available for use.

FossilOrigin-Name: 4b2c59acce6ff1bb6c9c04c45c80945ae23a26588718cc20635d60f7497adabb
diff --git a/src/trigger.c b/src/trigger.c
index 90e6ef4..c5beeb9 100644
--- a/src/trigger.c
+++ b/src/trigger.c
@@ -926,6 +926,7 @@
   sSelect.pSrc = &sFrom;
   sFrom.nSrc = 1;
   sFrom.a[0].pTab = pTab;
+  sFrom.a[0].iCursor = -1;
   sqlite3SelectPrep(pParse, &sSelect, 0);
   if( db->mallocFailed==0 && pParse->nErr==0 ){
     sqlite3GenerateColumnNames(pParse, &sSelect);