[ASan] Don't crash in DescribeHeapAddress if we don't know the current thread's ID
[ASan] Don't crash in DescribeHeapAddress if we don't know the current thread's ID

Also make DescribeThread easier to use.
This was firing on Dr.ASan runs, not sure how to repro InvalidTID in a simple test.

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@190392 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt