fix: fix when package equal service name

[Gcaufy]

In the proto file, if the service name === package name, then lookupService does not work.

Check here: https://github.com/protobufjs/protobuf.js/blob/master/src/namespace.js#L341-L358

When it found a matched name type, it will stop fetching the nestedArray.

Reproduce Code

// test.proto
package greeter;

syntax = "proto2";

service greeter {
    rpc SayHello (HelloRequest) returns (HelloReply) {}
}
message HelloRequest {
    optional string name = 1;
}
message HelloReply {
    optional string message = 1;
}

// test.js
const protobuf = require('protobufjs');
const root = protobuf.loadSync('./test.proto');
const svr = root.lookupService('greeter'); // This line will throw an Error

Error: no such Service 'greeter' in Root
    at Root.lookupService (/private/tmp/node_modules/protobufjs/src/namespace.js:426:15)
    at Object.<anonymous> (/private/tmp/test-proto-service/index.js:7:18)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
    at startup (internal/bootstrap/node.js:279:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:752:3)

[alexander-fenster]

Hi @Gcaufy,

Would you be willing to add a test for this scenario, and make sure the tests are green?

Thank you!

[alexander-fenster]

@Gcaufy Apparently one of the test fails with this change, the code is here:

protobuf.js/tests/api_namespace.js

Lines 38 to 40 in e8449c4

	test.throws(function() {
	ns.lookupType("Enm");
	}, Error, "should throw when looking up an enum as a type");

@murgatroid99 and I believe that the failing test might be wrong (it should've found the message Enm). Could you please make the tests pass, and probably add one more test for the case you're fixing?

[Gcaufy]

@alexander-fenster Tests updated. please take your time have a look.

[Gcaufy]

@alexander-fenster

Can you have a look the pull request?