Prevent floating images from breaking out of the message area

ref https://www.woltlab.com/community/thread/311517/

Author: BurntimeX

wcfsetup/install/files/style/layout/global.scss

@@ -202,6 +202,7 @@ ol.nativeList {
 		clear: both;
 		display: block;
 		margin: 1em auto;
+		max-width: 100%;
 		min-width: 50px;
 		text-align: center;