Link to PDF file (or attach file here):
https://issues.apache.org/jira/secure/attachment/12650283/000004_ShadingPatternTextPDF.pdf

Configuration:
- Web browser and its version: FF 51.0.1 32bit
- Operating system and its version: W7
- PDF.js version: latest

Steps to reproduce the problem:
display file

What is the expected behavior? (add screenshot)
![ok](https://cloud.githubusercontent.com/assets/6665575/23339534/5ff2de9c-fc25-11e6-837e-0fdaf81b4ca9.png)

What went wrong? (add screenshot)
![nok](https://cloud.githubusercontent.com/assets/6665575/23339536/63f7a37e-fc25-11e6-813c-cc218cc4def3.png)

possibly similar problem:
https://www.pdflib.com/fileadmin/pdflib/Cookbook/pdf/color_gradient.pdf (shaded text completely missing)
https://issues.apache.org/jira/secure/attachment/12630566/pslib-shading.pdf (page 4, part of text missing)
https://issues.apache.org/jira/secure/attachment/12652009/pattern-shading-2-4-idMatrix.pdf (some text missing)
https://issues.apache.org/jira/secure/attachment/12652010/pattern-shading-2-4-noMatrix.pdf (some text missing)

for (j = 0; j < thisChunkHeight; j++) {
        const srcDiff = srcLength - srcPos;
        let k = 0;
        const kEnd = srcDiff > fullSrcDiff ? width : srcDiff * 8 - 7;
        const kEndUnrolled = kEnd & ~7;
        let mask = 0;
        let srcByte = 0;
        for (; k < kEndUnrolled; k += 8) {
          srcByte = src[srcPos++];
          dest32[destPos++] = srcByte & 128 ? white : black;
          dest32[destPos++] = srcByte & 64 ? white : black;
          dest32[destPos++] = srcByte & 32 ? white : black;
          dest32[destPos++] = srcByte & 16 ? white : black;
          dest32[destPos++] = srcByte & 8 ? white : black;
          dest32[destPos++] = srcByte & 4 ? white : black;
          dest32[destPos++] = srcByte & 2 ? white : black;
          dest32[destPos++] = srcByte & 1 ? white : black;
        }
        for (; k < kEnd; k++) {
          if (mask === 0) {
            srcByte = src[srcPos++];
            mask = 128;
          }
          dest32[destPos++] = srcByte & mask ? white : black;
          mask >>= 1;
        }
      }
      
      while (destPos < dest32DataLength) {
        dest32[destPos++] = 0;