Bug 607361: Creating an attachment without a "comment" param in the URL causes an internal error

attachment.cgi

@@ -504,6 +504,7 @@ sub insert {
 
     # Insert a comment about the new attachment into the database.
     my $comment = $cgi->param('comment');
+    $comment = '' unless defined $comment;
     $bug->add_comment($comment, { isprivate => $attachment->isprivate,
                                   type => CMT_ATTACHMENT_CREATED,
                                   extra_data => $attachment->id });
@@ -639,7 +640,7 @@ sub update {
     # If the user submitted a comment while editing the attachment,
     # add the comment to the bug. Do this after having validated isprivate!
     my $comment = $cgi->param('comment');
-    if (trim($comment)) {
+    if (defined $comment && trim($comment) ne '') {
         $bug->add_comment($comment, { isprivate => $attachment->isprivate,
                                       type => CMT_ATTACHMENT_UPDATED,
                                       extra_data => $attachment->id });