Return early if it fails to parse a hex string.
Return early if it fails to parse a hex string.

This patch doesn't change the behavior of the program because it
would eventually return None at end of the function. But it is
better to return None early if we know it will eventually happen.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@315495 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld