fix: do not crash pfd when ls frequency = 0

[Saschl]

Fixes #[issue_no]

Summary of Changes

For a short moment, NAV FREQUENCY:3 can return 0 which crashes the PFD as it tries to split that frequency for displaying. This PR adds a check that the frequency is splitted correctly and aborts further execution if it's invalid.

Screenshots (if necessary)

References

Additional context

Discord username (if different from GitHub):

Testing instructions

Enable the LS info on the PFD and enter different ILS frequencies (in range, out of range, valid and invalid combinations) and make sure the PFD stays on all the time and shows valid information.

How to download the PR for QA

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[Hyper3007]

Quality Assurance Trainee Report

Discord : [CRSD] Andrew3007#0125
Object of testing: #6856
Tier of Testing : 1
Date : 05/03/2022

Testing Process:
Spawn in at EGWU on the runway entered frequency for EGWU, then i enter freq for EGLC, EGLL, EGKK, EGSS also enter, KJFK then re entered freq for EGWU again and repeated all those frequency a second time with 0 crashes to the PFD

Negatives:
N/A

Testing Results:
Passed

Conclusions:
No mattter what frequency i entered the PFD did not crash

Media:

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[NUTTTTTTTT]

Quality Assurance Tester Report

Discord: █▀█ █▄█ ▀█▀#2123
Object of testing: #PR 6856
Tier of Testing: 1
Date: 05/03/2022

Testing Process:

• Loaded at runway at EGKK.
• Tested local ILS, distance to navaid shown, LOC and GS diamonds shown as expected. - PASS
• Tested various other ILS frequencies, random number combinations, out of range frequencies et, tested for any PFD crashes - PASS.

Negatives: N/A

Testing Results: PASS.

Conclusions: No crashes to PFD. LGTM!

Media:

[FlightSimmer7700]

Quality Assurance Tester

Discord: FlightSimmer7700#5438
Object of testing: #6856
Tier of Testing: 1
Date: 5/3/22

Testing Process: Loaded C&D at LGAV and entered 110.5 (ils freq for LGAV) which worked and then entered 109.5 (not close) and checked captain's pfd didn't crash.
(Have also tested on dev to make sure that the same method did crash the pfd previously)
Negatives: N/A
Testing Results: Passed

Conclusions: Works as intended with no blank pfds!