[symbolizer] Treat invalid address as addr2line does

llvm-symbolizer echoed input if it was not recognized as a valid address.
This behavior was extended to llvm-addr2line as well. GNU addr2line in
this case optputs "??:0". This difference prevents implementation of
symbol+offset lookup available in the recent versions of GNU binutils.
In that case a string that is not an address may be a symbol.

This change make reaction of llvm-addr2line on unrecognized input closer
to GNU addr2line.