Guard against reading from host address of 0 in getting the data from a Value.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@204359 91177308-0d34-0410-b5e6-96231b3b80d8
Quiet Clang warning about signed/unsigned comparison


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@204360 91177308-0d34-0410-b5e6-96231b3b80d8