[ASan] Also print <empty stack> when size==0

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@195955 91177308-0d34-0410-b5e6-96231b3b80d8
Fix current stack unwinding when using DRASan

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@195956 91177308-0d34-0410-b5e6-96231b3b80d8