do not deref a NULL ptr


git-svn-id: svn+ssh://svn.code.sf.net/p/gphoto/code/trunk@14526 67ed7778-7388-44ab-90cf-0a291f65f57c
fixed some null ptr checks after deref (Coverity)


git-svn-id: svn+ssh://svn.code.sf.net/p/gphoto/code/trunk@14527 67ed7778-7388-44ab-90cf-0a291f65f57c