Getting the position of a non-position TOOL_EVENT will
now result in a wxCHECK, and a null-position (0,0) will
be returned. The new interface HasPosition() can be used
to determine if a call to a position function is safe to
make from the caller.
Fixes the underlying danger behind lp:1796045, which has
already been neutralised by a4966adb6, which avoids calling
the Position() functions when the TOOL_EVENT is not known
to be a position.
Fixes: lp:1796045
* https://bugs.launchpad.net/kicad/+bug/1796045
b64c6dbf35