tracking.html: Fixed bug with empty array
tracking.html: Fixed bug with empty array

An existing (not null) array that is empty caused a JavaScript
exception.

Signed-off-by: Rudolf J Streif <ea7b312ba06c558b2c165670d6c670057f7928aa@gmail.com>

PDXostc/rvi_backend,klooer/rvi_backend,klooer/rvi_backend,PDXostc/rvi_backend,rstreif/rvi_backend,PDXostc/rvi_backend,magnusfeuer/rvi_backend,lillialexis/rvi_backend,PDXostc/rvi_backend,bharmon/rvibackend,afan1/rvi_backend,magnusfeuer/rvi_backend,dvthiriez/rvi_backend,dvthiriez/rvi_backend,lillialexis/rvi_backend,dvthiriez/rvi_backend,magnusfeuer/rvi_backend,afan1/rvi_backend,rstreif/rvi_backend,magnusfeuer/rvi_backend,bharmon/rvibackend,rstreif/rvi_backend,klooer/rvi_backend,afan1/rvi_backend,bharmon/rvibackend,bharmon/rvibackend,rstreif/rvi_backend,klooer/rvi_backend,afan1/rvi_backend,lillialexis/rvi_backend,dvthiriez/rvi_backend,lillialexis/rvi_backend