[ptx] bug when opening directly a pto file

[Frédéric Da Vitoria]

Hello

I am using Hugin 0.5 rc1 on an XP Pro system.

If I open a .pto file, for example directly from Windows Explorer, Hugin 
starts with asking me what file I want to open, but if I first load 
Hugin and then ask it to open the pto file, it opens the images without 
asking any further question. This second behavior is of course much better.

-- 
Frederic Da Vitoria