Fix test failure in qqmldebugjs autotest

Fix test failure in qqmldebugjs autotest

The debugger should only have one breakpoint that can
be set per line. Nevertheless, we should have proper
line number information available in case we stop at
other places.

We also need a debug instruction before the return
statement, so that step out will always find a last
stopping point in the parent frame.

Change-Id: I86145fc244148f106a4a97ce69ab60b568c8dac6
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>