Avoid a crash in TStreamerInfo::Compile in the case where     a) the class on file inherit from an abstract class    b) the class in memory does no longer inherit from an abstract class    c) the abstract class is still loaded in memory In this case, it may happen that we do not have the StreamerInfo for the abstract base class when build the StreamerInfo for the onfile version of the class.
Avoid a crash in TStreamerInfo::Compile in the case where 
   a) the class on file inherit from an abstract class
   b) the class in memory does no longer inherit from an abstract class
   c) the abstract class is still loaded in memory
In this case, it may happen that we do not have the StreamerInfo for
the abstract base class when build the StreamerInfo for the onfile version
of the class.


git-svn-id: ecbadac9c76e8cf640a0bca86f6bd796c98521e3@41414 27541ba8-7e3a-0410-8455-c3a389f83636

dawehner/root,dawehner/root,dawehner/root,dawehner/root,dawehner/root,dawehner/root,dawehner/root,dawehner/root