Merge pull request #10724 from owncloud/min-size-for-icons

define min height/width for icon classes to make sure they show

core/css/icons.css

 [class^="icon-"], [class*=" icon-"] {
 	background-repeat: no-repeat;
 	background-position: center;
+	min-width: 16px;
+	min-height: 16px;
 }