Fix issue where we would double unwatch the path.

runtime/bin/file_system_watcher_macos.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/file_system_watcher.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 183 matching lines @@
  private:
   static void Callback(ConstFSEventStreamRef ref,
                        void* client,
                        size_t num_events,
                        void* event_paths,
                        const FSEventStreamEventFlags event_flags[],
                        const FSEventStreamEventId event_ids[]) {
     Node* node = reinterpret_cast<Node*>(client);
     for (size_t i = 0; i < num_events; i++) {
       char *path = reinterpret_cast<char**>(event_paths)[i];
-      path += node->base_path_length() + 1;
+      path += node->base_path_length();
+      // If path is longer the base, skip next character ('/').
+      if (path[0] != '\0') path += 1;
       if (!node->recursive() && strstr(path, "/") != NULL) continue;
       FSEvent event;
       event.data.flags = event_flags[i];
       memmove(event.data.path, path, strlen(path) + 1);
       write(node->write_fd(), event.bytes, sizeof(event));
     }
   }
 
   CFRunLoopRef run_loop_;
   int users_;
@@ skipping 70 matching lines @@
   }
   return events;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)