patch 8.1.2401: :cexpr does not handle | in expression

Problem:    :cexpr does not handle | in expression.
Solution:   Remove EX_TRLBAR and set nextcmd pointer.
diff --git a/src/quickfix.c b/src/quickfix.c
index 3d12374..206e901 100644
--- a/src/quickfix.c
+++ b/src/quickfix.c
@@ -7548,7 +7548,7 @@
 
     // Evaluate the expression.  When the result is a string or a list we can
     // use it to fill the errorlist.
-    tv = eval_expr(eap->arg, NULL);
+    tv = eval_expr(eap->arg, &eap->nextcmd);
     if (tv != NULL)
     {
 	if ((tv->v_type == VAR_STRING && tv->vval.v_string != NULL)