Fix relative path issue on Win32

ssdeep on Win32 fails to open files if relative path option `-l' is
given. This is due to inconsistent path handling on engine.cpp and this
commit will fix this issue.

This bug is reported by Robert Engelhardt.

engine.cpp

@@ -63,7 +63,7 @@ int hash_file(state *s, TCHAR *fn) {
 
 #ifdef WIN32  
   TCHAR expanded_fn[SSDEEP_PATH_MAX];
-  if (not expanded_path(fn)) {
+  if (not expanded_path(fn) && !(s->mode & mode_relative)) {
     _sntprintf(expanded_fn, 
 	       SSDEEP_PATH_MAX,
 	       _TEXT("\\\\?\\%s"),