Fixes issue with TMath::BreitWigner not being visible as a decl of its context.


git-svn-id: https://root.cern.ch/svn/root/branches/dev/root6-pch@48916 27541ba8-7e3a-0410-8455-c3a389f83636
Don't set NMethods to 0 *before* checking whether an update is needed.
An empty context is fine and no reason to update the method count.
Fix iteration over secls in context: use decls_end().


git-svn-id: https://root.cern.ch/svn/root/branches/dev/root6-pch@48917 27541ba8-7e3a-0410-8455-c3a389f83636