Horizontal Scroll Bar does not work correctly with LineNumberFactory

[atsepushel]

Expected Behavior

CodeArea always showing caret (scrolling to visible) on keyboard moving (left/right buttons)

Actual Behavior

CodeArea not showing caret on keyboard moving (left/right buttons). Scroll begin moving only after few keyboard "right" button clicks, looks depended on LineNumberFactory nodes width

Reproducible Demo

• Your default JavaKeywordsDemo.java
• Run and change window width for showing horizontal scroll bar
• 
• Set caret position to the end of the line that is not fully visible and tries move with the keyboard to the right
• Visible area begin moving only after few buttons button clicks

Environment info:

• RichTextFX Version: 0.10.6
• Operating System: Windows 10
• Java version: 1.8.0_112

[appsofteng]

The line number label must move by breadth offset when the view port moves. Currently the offset is updated several times and one update is 0 which keeps the line number at the beginning of the virtual flow.
The solution I used is to prevent multiple offset update by removing and then adding listeners in org.fxmisc.flowless.VirtualizedScrollPane
This prevents event cycling.

Original:

    private final ChangeListener<Double> hbarValueListener;
    private final ChangeListener<Double> hPosEstimateListener;
    private Var<Double> hbarValue;
    private Var<Double> hPosEstimate;

    hbarValueListener = (observable, oldValue, newValue) -> hPosEstimate.setValue(newValue);
    hbarValue.addListener(hbarValueListener);
    hPosEstimateListener = (observable, oldValue, newValue) -> hbarValue.setValue(newValue);
    hPosEstimate.addListener(hPosEstimateListener);

Changed:

    private ChangeListener<Double> hbarValueListener;
    private ChangeListener<Double> hPosEstimateListener;
    private Var<Double> hbarValue;
    private Var<Double> hPosEstimate;

    hbarValueListener = (observable, oldValue, newValue) -> {
	hPosEstimate.removeListener(hPosEstimateListener);
        hPosEstimate.setValue(newValue);
        hPosEstimate.addListener(hPosEstimateListener);
    };
    hbarValue.addListener(hbarValueListener);

    hPosEstimateListener = (observable, oldValue, newValue) -> {
        hbarValue.removeListener(hbarValueListener);
        hbarValue.setValue(newValue);
        hbarValue.addListener(hbarValueListener);
    };
    hPosEstimate.addListener(hPosEstimateListener);

[Jugen]

@appsofteng thanks very much for this, have submitted a PR in Flowless to fix this.