[NaCl SDK] nacl_io: Fix bug in Path::Range introduced in recent change.

native_client_sdk/src/libraries/nacl_io/path.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "nacl_io/path.h"
 
 #include <assert.h>
 #include <stdio.h>
 #include <string.h>
 #include <string>
@@ skipping 152 matching lines @@
       if (slashes == start)
         pstart = p + 1;
 
       if (slashes == end) {
         pend = p;
         break;
       }
     }
   }
 
-  if (pstart > pend)
+  if (slashes < start || pstart > pend)
     return std::string();
 
   return std::string(pstart, pend - pstart);
 }
 
 void Path::Normalize() {
   char* outp = &path_[0];
   const char* start = outp;
   const char* part_start = start;
   const char* next_slash;
@@ skipping 79 matching lines @@
 
 bool Path::operator==(const Path& other) {
   return len_ == other.len_ && strncmp(path_, other.path_, len_) == 0;
 }
 
 bool Path::operator!=(const Path& other) {
   return !operator==(other);
 }
 
 }  // namespace nacl_io