Fix coverity issues

Dereference null return:
32943,32945,36325,36329: TFormLeafInfo::GetLocalValuePointer
33253: TTreeFormula::EvalObject
33763: CloneTree
33258: GetBasket
34034: In DropBuffers (in addition avoid reading the basket when the intend is to drop the content from memory!)
36307: TTree::BuildIndex
36328: DrawCopy
36332: GetStreamerInfoCache
33025: BuildStreamerInfo
42469: Clone
33436: MakeIterator
Dereference after null check.
42470: in ImportStreamerInfo
33138: in TEntryListArray::Enter
Unchecked return value:
32049, 32050: TBranchProxy::Read and Setup
Mixed enums:
32705,32706: TClass::fStreamerType (and also name the enum type).


git-svn-id: http://root.cern.ch/svn/root/trunk@43993 27541ba8-7e3a-0410-8455-c3a389f83636