[sanitizer] Detect an invalid answer in AtosSymbolizer

On OS X, in AtosSymbolizer, if the answer from atos doesn't contain module name, let's bail and return false. There are some cases where this is beneficial, because we'll try DlAddrSymbolizer next (it's next in the symbolizer chain), which might be able to symbolize something that atos couldn't.

Differential Revision: http://reviews.llvm.org/D15071

llvm-svn: 254301