Attach (recommended) or Link to PDF file here:
https://bitcoin.org/bitcoin.pdf

Configuration:
- Web browser and its version: all
- Operating system and its version: all
- PDF.js version: tested with 2.9.11, but most likely all versions
- Is a browser extension: no

Steps to reproduce the problem:
1. Type "a purely" (single space between "a" and "purely") - doesn't find anything
2. Type "a  purely" (two spaces between "a" and "purely") - finds the phrase

Sometimes even 3 spaces are necessary.

What is the expected behavior? (add screenshot)
![Screenshot from 2021-04-08 13-00-03](https://user-images.githubusercontent.com/6362989/114008903-57639a00-986b-11eb-903a-92bbebbd922b.png)

What went wrong? (add screenshot)
![Screenshot from 2021-04-08 13-01-53](https://user-images.githubusercontent.com/6362989/114008810-44e96080-986b-11eb-8232-f58a62ed7899.png)

This affects many PDFs because justify alignment is common enough.
const textDivProperties = this._textDivProperties.get(textDiv);
    let transform = "";
    if (textDivProperties.canvasWidth !== 0 && textDivProperties.hasText) {
      const { fontSize, fontFamily } = textDiv.style;
      
      if (
        fontSize !== this._layoutTextLastFontSize ||
        fontFamily !== this._layoutTextLastFontFamily
      ) {
        this._layoutTextCtx.font = `${fontSize} ${fontFamily}`;
        this._layoutTextLastFontSize = fontSize;
        this._layoutTextLastFontFamily = fontFamily;
      }
      
      const { width } = this._layoutTextCtx.measureText(textDiv.textContent);