Fixing an issue with cache disabling

Changes

• Fixed a bug where if you disabled connection caching and tried to source() twice at the same time on the same path, the second source would fail due to an internal aggressive semaphore.
  So in this case

  const sse1 = source('/events', { cache: false }).select('message');
  const sse2 = source('/events', { cache: false }).select('message');

  sse2 would fail to connect silently.