fix: Handle fallback video format on CourseUnitNavigationActivity

[omerhabib26]

Description

LEARNER-9658

• Show fallback video in case course doesn't have any video quality available

[codecov]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (bcf1d6d) 1.08% compared to head (d4f8b34) 1.07%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##             master   #1835      +/-   ##
===========================================
- Coverage      1.08%   1.07%   -0.01%     
  Complexity      137     137              
===========================================
  Files           538     538              
  Lines         26293   26299       +6     
  Branches       3381    3383       +2     
===========================================
  Hits            284     284              
- Misses        25982   25988       +6     
  Partials         27      27              

Files	Coverage Δ
...a/org/edx/mobile/model/course/VideoBlockModel.java	10.71% <0.00%> (-0.40%)	⬇️
...org/edx/mobile/module/db/DatabaseModelFactory.java	0.00% <0.00%> (ø)

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[farhan-arshad-dev]

Able to reproduce the crash for the course having fallback videos. and this code change fixes the crash. 🏎️ 🔥