Fix bug #48695 - Do not try to create thumbnails for images we cannot open properly.

git-svn-id: file:///svn/phpbb/branches/phpBB-3_0_0@9899 89ea8834-ac86-4346-8a33-228a782c2dd0

phpBB/includes/functions_posting.php

@@ -696,6 +696,11 @@ function create_thumbnail($source, $destination, $mimetype)
 				break;
 			}
 
+			if (empty($image))
+			{
+				return false;
+			}
+
 			if ($type['version'] == 1)
 			{
 				$new_image = imagecreate($new_width, $new_height);