Reset onerror on images if placeholder does not exist to prevent from requests storm

program/steps/addressbook/func.inc

@@ -860,7 +860,7 @@ function rcmail_contact_photo($attrib)
     $content = html::div($attrib, html::img(array(
             'src'     => $photo_img,
             'alt'     => $RCMAIL->gettext('contactphoto'),
-            'onerror' => 'this.src = rcmail.env.photo_placeholder',
+            'onerror' => 'this.src = rcmail.env.photo_placeholder; this.onerror = null',
     )));
 
     if ($CONTACT_COLTYPES['photo'] && ($RCMAIL->action == 'edit' || $RCMAIL->action == 'add')) {

program/steps/mail/show.inc

@@ -336,7 +336,7 @@ function rcmail_message_contactphoto($attrib)
             '_email'  => $MESSAGE->sender['mailto'],
         ));
 
-        $attrib['onerror'] = "this.src = '$placeholder'";
+        $attrib['onerror'] = "this.src = '$placeholder'; this.onerror = null";
     }
     else {
         $photo_img = $placeholder;

program/steps/settings/func.inc

@@ -353,7 +353,7 @@ function rcmail_user_prefs($current = null)
                                 'alt'     => $skin,
                                 'width'   => 64,
                                 'height'  => 64,
-                                'onerror' => "this.src = rcmail.assets_path('program/resources/blank.gif')",
+                                'onerror' => "this.src = rcmail.assets_path('program/resources/blank.gif'); this.onerror = null",
                         ));
 
                         $skinnames[] = mb_strtolower($skinname);