Attach (recommended) or Link to PDF file here:
[298865.pdf](https://github.com/mozilla/pdf.js/files/2753236/298865.pdf)


Configuration:
- Web browser and its version:chrome 71.0.3578.98
- Operating system and its version:mac os 10.12.6
- PDF.js version:I use online demo in github
- Is a browser extension:no

Steps to reproduce the problem:
1. search "中华" or "电力" or so on,the highlight position is not right

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/10000986/51087378-7eff5100-178d-11e9-991a-005d77b82f31.png)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/10000986/51087374-6ee77180-178d-11e9-9707-281924f95fd0.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):
https://mozilla.github.io/pdf.js/web/viewer.html
describe("Page", function () {
    let pdfLoadingTask, pdfDocument, page;
    beforeAll(async function () {
      pdfLoadingTask = getDocument(basicApiGetDocumentParams);
      pdfDocument = await pdfLoadingTask.promise;
      page = await pdfDocument.getPage(1);
    });
    afterAll(async function () {
      await pdfLoadingTask.destroy();
    });
    it("gets page number", function () {
      expect(page.pageNumber).toEqual(1);
    });
    it("gets rotate", function () {
      expect(page.rotate).toEqual(0);
    });
    it("gets ref", function () {
      expect(page.ref).toEqual({ num: 15, gen: 0 });
    });
    it("gets userUnit", function () {
      expect(page.userUnit).toEqual(1.0);
    });
    it("gets view", function () {
      expect(page.view).toEqual([0, 0, 595.28, 841.89]);
    });
    it("gets view, with empty/invalid bounding boxes", async function () {
      const viewLoadingTask = getDocument(
        buildGetDocumentParams("boundingBox_invalid.pdf")
      );
      const pdfDoc = await viewLoadingTask.promise;