Make autoreload robust to syntax errors and empty apps

[philippjfr]

Fixes #6649

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 8 lines in your changes missing coverage. Please review.

Project coverage is 82.20%. Comparing base (c6d0ff3) to head (36d3f9b).

Files	Patch %	Lines
panel/io/handlers.py	77.27%	5 Missing ⚠️
panel/command/serve.py	66.66%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7028      +/-   ##
==========================================
- Coverage   82.22%   82.20%   -0.03%     
==========================================
  Files         326      326              
  Lines       48236    48254      +18     
==========================================
+ Hits        39663    39667       +4     
- Misses       8573     8587      +14     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[MarcSkovMadsen]

Thx. Been dreaming about this for a Long time.

[philippjfr]

Same, well overdue!