Replace instanceof Object with typeof checks

[Snuffleupagus]

Using instanceof Object is generally problematic, since it's not guaranteed to always do the right thing for all Objects.
(I stumbled upon this while working on another patch, when I noticed that the outlineView was broken with workers disabled.)

[Snuffleupagus]

/botio test

[pdfjsbot]

From: Bot.io (Windows)

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Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://3.101.106.178:8877/246445bae803c28/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

---

Received

Command cmd_test from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.67.70.0:8877/1903cc3620eb60f/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

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Failed

Full output at http://54.67.70.0:8877/1903cc3620eb60f/output.txt

Total script time: 30.38 mins

• Font tests: Passed
• Unit tests: Passed
• Integration Tests: Passed
• Regression tests: FAILED

  different ref/snapshot: 9
  different first/second rendering: 1

Image differences available at: http://54.67.70.0:8877/1903cc3620eb60f/reftest-analyzer.html#web=eq.log

[pdfjsbot]

From: Bot.io (Windows)

---

Failed

Full output at http://3.101.106.178:8877/246445bae803c28/output.txt

Total script time: 34.81 mins

• Font tests: Passed
• Unit tests: Passed
• Integration Tests: Passed
• Regression tests: FAILED

  different ref/snapshot: 9
  different first/second rendering: 1

Image differences available at: http://3.101.106.178:8877/246445bae803c28/reftest-analyzer.html#web=eq.log

[timvandermeij]

/botio-linux preview

[pdfjsbot]

From: Bot.io (Linux m4)

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Received

Command cmd_preview from @timvandermeij received. Current queue size: 0

Live output at: http://54.67.70.0:8877/915f52a0e39bc28/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.67.70.0:8877/915f52a0e39bc28/output.txt

Total script time: 5.05 mins

Published

• Viewer: http://54.67.70.0:8877/915f52a0e39bc28/web/viewer.html
• Viewer (legacy): http://54.67.70.0:8877/915f52a0e39bc28/legacy/web/viewer.html

[timvandermeij]

I couldn't immediately figure out from the given description in which cases this would fail, but some Googling showed me that this happens for objects without prototypes, which we use. From the console:

> const foo = Object.create(null);
undefined
> foo instanceof Object
false
> typeof foo === "object" && foo !== null
true

I'm adding this for future reference.

[timvandermeij]

Thanks!

[Snuffleupagus]

I couldn't immediately figure out from the given description in which cases this would fail,

My apologies; I should have included more details in the commit message!