Fix improper use of isNil in fn_equipRebel

[jwoodruff40]

What type of PR is this?

• Bug
• Change
• Feature
• Miscellaneous

Sub-categories:

• Template
• Map
• Config
• Function
• Localization

What have you changed, and why?

Information:

Title. Can cause script error when a template doesn't add map, compass, or watch to IRE causing unlockedMaps, unlockedCompasses, or unlockedWatches to be [].

How can your changes be tested, or reproduced?

Load new game with GM FIA rebel faction. Use quick equip loadout function on arsenal and ensure no script error.

Does this PR include changes not authored by you?

• No
• Yes (See below)

Further info:

• I confirm that I, and by extension this repository, can legally use these third-party changes. (Provide links or author attribution.)

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Please verify the following (If possible).

* - Mandatory

• These changes are my own, or I have written permission to use them. *
• These changes are ready for review, or will be marked as a draft. *
• I have loaded the mission in LAN host.
• I have loaded the mission on a dedicated server.

Is further work needed?

• Needs further testing.
• Needs further changes.
• Needs to be converted to a draft.

Please specify which Issue this PR Resolves (If Applicable).

This PR closes #XYZ.

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Notes:

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