qt a11y: Check range for offset passed to text methods

Otherwise LO crashes when invalid offsets are passed
from AT when using the qt5/qt6/kf5 VCL plugins.

One scenario that resulted in a crash:

* start Accerciser
* start Calc
* press F2 in cell A1 to enter edit mode
* navigate to the "Cell A1" object representing the
editable cell, then to its paragraph child in
Accerciser's treeview of the LO a11y hierarchy
* in Accerciser's "Interface Viewer", type
Enter, then any character

This would crash due to a
`com::sun::star::lang::IndexOutOfBoundsException`
being thrown by one of the methods of the
XAccessibleText/XAccessibleEditableText
interfaces.

Change-Id: I1b8c6057ca1e4e4485d516418bb82cd1a6697ce1
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/138078
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

0 files changed, 0 insertions, 0 deletions