[analyzer] NullOrUndef diagnostics: track symbols binded to regions.

If a region is binded to a symbolic value, we should track the symbol.

(The code I changed was not previously exercised by the regression
tests.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@163261 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed