[tools] testbot/web: Use AddError() in the failure details page.

[Francois Gouget]

This is better than direct field access.

Signed-off-by: Francois Gouget 
---
 testbot/web/FailureDetails.pl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/testbot/web/FailureDetails.pl b/testbot/web/FailureDetails.pl
index 02803ed27a..b4226f60c5 100644
--- a/testbot/web/FailureDetails.pl
+++ b/testbot/web/FailureDetails.pl
@@ -203,7 +203,7 @@ sub OnAction($$)
   {
     if (!$self->{RW})
     {
-      $self->{ErrMessage} = "Only admin users can create or modify failures";
+      $self->AddError("Only admin users can create or modify failures");
       return 0;
     }
     if (($self->{Item}->BugId || "") ne $self->GetParam("BugId"))