loadSync: should load a test file that relies on common protos failed

[flaky-bot]

This test failed!

To configure my behavior, see the Flaky Bot documentation.

If I'm commenting on this issue too often, add the flakybot: quiet label and
I will stop commenting.

---

commit: c8df19d
buildURL: Build Status, Sponge
status: failed

Test output

error reading first path in the walk /workspace/google/protobuf
Error: ENOENT: no such file or directory, lstat '/workspace/google/protobuf'
Error: error reading first path in the walk /workspace/google/protobuf
Error: ENOENT: no such file or directory, lstat '/workspace/google/protobuf'
    at EventEmitter. (node_modules/walkdir/walkdir.js:265:28)
    at fn (node_modules/walkdir/walkdir.js:100:17)
    at statter (node_modules/walkdir/walkdir.js:137:7)
    at walkdir (node_modules/walkdir/walkdir.js:269:3)
    at Function.walkdir.sync (node_modules/walkdir/walkdir.js:15:10)
    at /workspace/build/src/load.js:43:29
        -> /workspace/src/load.ts:50:24
    at Array.map ()
    at Function.getCommonProtoFiles (build/src/load.js:42:18)
        -> /workspace/src/load.ts:49:10
    at GoogleProtoFilesRoot.resolvePath (build/src/load.js:60:55)
        -> /workspace/src/load.ts:71:51
    at process (node_modules/protobufjs/src/root.js:132:86)
    at fetch (node_modules/protobufjs/src/root.js:178:13)
    at GoogleProtoFilesRoot.load (node_modules/protobufjs/src/root.js:206:13)
    at GoogleProtoFilesRoot.loadSync (node_modules/protobufjs/src/root.js:247:17)
    at Object.loadSync (build/src/load.js:70:17)
        -> /workspace/src/load.ts:83:15
    at Context. (build/test/load.test.js:58:39)
        -> /workspace/test/load.test.ts:73:35
    at processImmediate (internal/timers.js:461:21)

[hkdevandla]

@summer-ji-eng , can you please take a look?

[summer-ji-eng]

fixed PR #426