Per offline discussion with Doug, don't perform typo correction when we have...

Per offline discussion with Doug, don't perform typo correction when we have encountered a fatal error.  On some files that are woefully wrong (missing headers) this can cause a 3x slowdown in some cases when parsing the file.  It makes sense not to perform typo correction in this case because after a fatal error diagnostics will either be suppressed or not really make any sense.

llvm-svn: 92809