intel/tools: fix initial position of window in aubinator viewer

intel/tools: fix initial position of window in aubinator viewer

Currently position is set before widgets are sized by gtk and
calculation can get wrong results where window is positioned
offscreen. Patch fixes this by setting aubfile window position
as 0,0 only when size_allocate has been called to the widget.

Now window is always positioned to 0,0 if imgui.ini is missing.

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>