Run the column cache in a new context when generating code for trigger
programs.  Fix for ticket [efc02f9779].

FossilOrigin-Name: dee1b8eb402f47c6d5ee60aac28f8e3dcf98167f
diff --git a/src/trigger.c b/src/trigger.c
index 893ebcb..eb84d9b 100644
--- a/src/trigger.c
+++ b/src/trigger.c
@@ -856,7 +856,9 @@
       sqlite3ExprIfFalse(pParse, whenExpr, endTrigger, SQLITE_JUMPIFNULL);
       sqlite3ExprDelete(db, whenExpr);
 
+      sqlite3ExprCachePush(pParse);
       codeTriggerProgram(pParse, p->step_list, orconf); 
+      sqlite3ExprCachePop(pParse, 1);
 
       /* Pop the entry off the trigger stack */
       pParse->trigStack = trigStackEntry.pNext;