Checkbox graphic disappears when siblings collapse

[calebbraun]

When a collapsable directory is listed in one of the file views, collapsing it causes the graphic of other (lower) files to disappear.

This bug is known about and mentioned in the following places without solution:

• https://stackoverflow.com/questions/28960294/javafx-checkboxtreeitem-graphic-disappears-if-graph-is-extended
• https://stackoverflow.com/questions/33621772/javafx-checkboxtreeitem-graphic-disappear-when-siblings-collapse
• https://bugs.openjdk.java.net/browse/JDK-8094112