fix(mcdu): Disable alternate time predictions if fuel manually specified

[BravoMike99]

Fixes #[issue_no]

Summary of Changes

Alternate time predictions become dashed in FUEL PRED & INIT FUEL PRED pages if fuel is specified manually.

Screenshots (if necessary)

Old & new

References

H3/H4 FCOM
https://youtu.be/efQlfF87c8c?t=205

Additional context

Discord username (if different from GitHub):
bruno_pt99

Testing instructions

Manually specify a alternate fuel value in the INIT B & and make sure the time prediction becomes dashed then delete the value and verify that the prediction comes back.
Manually specify an alternate fuel value in the FUEL PRED Page ( only available after engines running) and verify that the time at the top of the page and next to the fuel prediction becomes dashed.
Clear the manually inserted value and make sure time becomes available on both fields

How to download the PR for QA

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[alepouna]

QA Report

Discord: alepouna
Object of testing: #8273
Tier of Testing : 1
Date : 02/11/2023

Testing Process:

• [PASS] Manually specify a alternate fuel value in the INIT B & and make sure the time prediction becomes dashed then delete the value and verify that the prediction comes back.
• [PASS] Manually specify an alternate fuel value in the FUEL PRED Page ( only available after engines running) and verify that the time at the top of the page and next to the fuel prediction becomes dashed.
• [PASS] Clear the manually inserted value and make sure time becomes available on both fields

Testing Results:
Passed