fix: multi-page demo & RGB for pdf reader

[charlesmindee]

This PR fixes 2 bugs spotted on the demo:

• multi-pages pdf were crashing the app
• pdf reader as images was outputing BGR instead of RGB

Any feedback is welcome!

[codecov]

Codecov Report

Merging #276 (3072b91) into main (f959be6) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #276   +/-   ##
=======================================
  Coverage   96.94%   96.94%           
=======================================
  Files          48       48           
  Lines        1966     1966           
=======================================
  Hits         1906     1906           
  Misses         60       60           

Flag	Coverage Δ
unittests	96.94% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
doctr/documents/reader.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f959be6...3072b91. Read the comment docs.

[fg-mindee]

Thanks for the fix!