[tools] testbot/cgi: Allow calling AddError() without an error.

[Francois Gouget]

This simplifies error handling for APIs that just return an error
message.

Signed-off-by: Francois Gouget <fgouget at codeweavers.com>
---
 testbot/lib/ObjectModel/CGI/Page.pm | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/testbot/lib/ObjectModel/CGI/Page.pm b/testbot/lib/ObjectModel/CGI/Page.pm
index 1df5392930..a8268754ac 100644
--- a/testbot/lib/ObjectModel/CGI/Page.pm
+++ b/testbot/lib/ObjectModel/CGI/Page.pm
@@ -356,6 +356,7 @@ Sets the error message to be shown to the user.
 =item ErrMessage
 A message to be shown on the page that describes why the form data is invalid.
 This should include the display name of the field(s) that need to be fixed.
+If this parameter is false the error message is not modified.
 
 =item ErrField
 If the error concerns a specific field, the name of that field. This can be
@@ -363,6 +364,9 @@ used by the page to highlight the field that needs to be corrected.
 
 =back
 
+Returns the ErrMessage parameter. This allows checking whether an error
+was actually added.
+
 =back
 =cut
 
@@ -370,8 +374,12 @@ sub AddError($$;$)
 {
   my ($self, $ErrMessage, $ErrField) = @_;
 
-  $self->{ErrMessage} = $ErrMessage;
-  $self->{ErrField} = $ErrField;
+  if ($ErrMessage)
+  {
+    $self->{ErrMessage} = $ErrMessage;
+    $self->{ErrField} = $ErrField;
+  }
+  return $ErrMessage;
 }
 
 # FIXME: For legacy code, to be removed.
-- 
2.30.2