Fix icon alignment in filepicker

Apply the patch. Select the 'Clean' theme. On a course add an file submissions assignment. Open up that assignment as a student on the course and click on 'Add submission'. Drag and drop a file to upload. Using the window resizing control gradually reduce the screen width until the 'Display folder icons' are forced onto the next line because of lack of space. Observe that the containing box expands to accommodate without rendering a line underneath them.