fix(driver): readFile - verify null contents to Buffer.from

[emilyrohrbough]

• Closes Adding null as an encoding argument to cy.readFile command results in TypeError #20683
  When null encoding is used, and a file cannot be found, we are passing null to Buffer.from which is throwing TypeError: First argument must be a string, Buffer, ArrayBuffer, Array, or array-like object. This caused the command to bail instead of retrying and providing a meaningful error message to the users.

User facing changelog

• Fixed an issue in cy.readFile() where the command would not retry or provide a meaningful error message if null encoding was used and the file was not found. Fixed #20683.

How has the user experience changed?

before	after

PR Tasks

• Have tests been added/updated?
• Has the original issue (or this PR, if no issue exists) been tagged with a release in ZenHub? (user-facing changes only)
• [n/a] Has a PR for user-facing changes been opened in cypress-documentation?
• [n/a] Have API changes been updated in the type definitions?
• [n/a] Have new configuration options been added to the cypress.schema.json?

[cypress-bot]

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[cypress]

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Test summary

218 • 0 • 1 • 0 • 0

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Run details

Project	cypress
Status	Passed
Commit	c6eb90c
Started	Mar 18, 2022 6:34 PM
Ended	Mar 18, 2022 6:43 PM
Duration	09:20 💡
OS	Linux Debian - 10.10
Browser	Firefox 93

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[cypress-bot]

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