Attach (recommended) or Link to PDF file here:
[backgroundimage_not_visible_anonymisiert.pdf](https://github.com/mozilla/pdf.js/files/6544725/backgroundimage_not_visible_anonymisiert.pdf)


Configuration:
- Web browser and its version: Chrome Version 90.0.4430.212 (Offizieller Build) (x86_64)
- Operating system and its version: Windows 10, MacOs BigSur
- PDF.js version: 2.5.207
- Is a browser extension: no

Steps to reproduce the problem:
1. open the document in demo viewer.js
2.

What is the expected behavior? (add screenshot)
The backgroundimage gets rendered like in Acrobat Reader
<img width="1348" alt="Bildschirmfoto 2021-05-26 um 09 44 21" src="https://user-images.githubusercontent.com/1286150/119621970-00a82480-be07-11eb-8fed-f74ac04b840b.png">

What went wrong? (add screenshot)
Backgroundimage is not rendered only some  text
<img width="987" alt="Bildschirmfoto 2021-05-26 um 09 43 57" src="https://user-images.githubusercontent.com/1286150/119621938-fab24380-be06-11eb-92ac-4ecb2c9334b1.png">




Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

for (i = 0; i < totalChunks; i++) {
        thisChunkHeight =
          i < fullChunks ? FULL_CHUNK_HEIGHT : partialChunkHeight;
        destPos = 0;
        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;
          }