Avoid add unnecessary ParseDecompressInterceptor

[wangmengyan95]

Fixes #355
We set network interceptor like this, when developers do not add external interceptors, parameter interceptors is null

 initialize(builder.setNetworkInterceptors(interceptors)
    .setLocalDatastoreEnabled(isLocalDatastoreEnabled)
    .build()
 );

link

For the Configuration.builder, its interceptors will never be null

/* package for tests */ Builder setNetworkInterceptors(Collection<ParseNetworkInterceptor> interceptors) {
  if (this.interceptors == null) {
    this.interceptors = new ArrayList<>();
  } else {
    this.interceptors.clear();
  }

  if (interceptors != null) {
    this.interceptors.addAll(interceptors);
  }
  return this;
}

link

Thus, in Parse.initialize(), the checking is actually useless since configuration.interceptors will never be null. This will make us always add ParseDecompressInterceptor.

// If we have interceptors in list, we have to initialize all http clients and add interceptors
if (configuration.interceptors != null) {
  initializeParseHttpClientsWithParseNetworkInterceptors(configuration.interceptors);
}

link.

To fix this, we should also check the size of the list.
cc @richardjrossiii

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By analyzing the blame information on this pull request, we identified @richardjrossiii, @grantland and @wangmengyan95 to be potential reviewers.

[grantland]

LGTM

[facebook-github-bot]

@wangmengyan95 updated the pull request.