[analyzer] Fix a regression in ObjCUnusedIVars checker.

We can no longer rely on children iterator to visit all the AST
tree children of an expression (OpaqueValueExpr has no children).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156870 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed