[patch] fix crashes when source applet of extender is removed

[Sebastian Kügler]

I've run into two subsequent crashes in extenderitem.cpp, those are 
reproducible for me as follows:

- d&d an extenderitem from an applet onto the desktop (it creates its own    
  applet then)
- Remove the source applet
- Remove the newly created extenderapplet
- Boom (in the check for d->sourceApplet
- Boom (setExtender(d->sourceApplet->d->extender);)

The attached patch fixes both. One issue I've run into is that the source 
applet still seems to own the content of the extenderitem. When removing the 
source applet, it goes away. So I'm wondering if it makes sense at all to keep 
the extenderitem around when the source applet goes away and takes the content 
of the extenderitem with it into Nirvana. It would be cool if that worked 
somehow, though.

In any case, plasma-desktop shouldn't crash, so OK to commit? Should it be 
backported?
-- 
sebas

 http://www.kde.org | http://vizZzion.org |  GPG Key ID: 9119 0EF9 

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