dragging point outside the board

[Christophe Bansart]

Hello,

I've identified a specific issue with JSXGraph's mobile points that occurs exclusively on mobile devices (tested on iPad and iPhone).

Issue Description

When interacting with a draggable point on a JSXGraph board, the point can be moved outside the visible board area on the left side, but remains properly constrained on the right side. This inconsistent behavior creates usability problems for mobile users.

Steps to Reproduce

1. Open this JSFiddle example on an iOS device (iPad or iPhone): https://jsfiddle.net/chrisb06/jo2p7wq1/21/
2. Touch the red mobile point and drag it toward the left edge of the board
3. Continue dragging left - the point will disappear beyond the board's boundary and continue to move outside the visible area
4. Reset the page and try the same operation, but drag to the right edge
5. Note that the point stops at the right boundary as expected

This behavior has been confirmed on multiple iOS versions and devices. The same code works correctly on desktop browsers, where the point remains properly constrained on both sides.

Thanks for your help

Chris