QmlProfiler: Off-by-one when calculating row offsets

Change-Id: I255f3e15e0afc0761a6d3c9a32955d007cd3b637
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
QmlProfiler: Show placeholder labels in select locations

The "<bytecode>" and "Source code not available" labels should not be
added to the model as otherwise they end up in trace files. Instead the
view should show them instead of empty strings where it makes sense.

Change-Id: I37a0c8468ead0194771556d9276c24cb7f05c061
Reviewed-by: Kai Koehne <kai.koehne@digia.com>