pipeCmd.join sometimes chrashes with selection exceptions

[rkrenzler]

When I test the "join pipes"-command I often get this message:

Traceback (most recent call last):
File "/home/ose-developer/.FreeCAD/Mod/flamingo/pipeObservers.py", line 75, in addSelection
sel=FreeCADGui.Selection.getSelection()[0]
<type 'exceptions.IndexError'>: list index out of range