Fix: Initialise button after adapter setup in UnitNavigationActivity

[omerhabib26]

Description

LEARNER-9653

• Initialise Navigation buttons after Pager Adapter initialisation on CourseUnitNavigation Activity

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (bcf1d6d) 1.08% compared to head (adaeee2) 1.08%.

Additional details and impacted files

@@           Coverage Diff            @@
##             master   #1832   +/-   ##
========================================
  Coverage      1.08%   1.08%           
  Complexity      137     137           
========================================
  Files           538     538           
  Lines         26293   26293           
  Branches       3381    3381           
========================================
  Hits            284     284           
  Misses        25982   25982           
  Partials         27      27           

Files	Coverage Δ
...obile/view/app_nav/CourseUnitNavigationActivity.kt	0.00% <0.00%> (ø)

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[farhan-arshad-dev]

Unable to reproduce this issue during the manual testing, so following the crash logs, and current code change looks appropriate to fix the crash.