disallow submission when files uploaded, but none valid

[naknomum]

this is a "fix" which blocks (classic/servlet) encounter submission when files are sent from the form, but all of them are invalid.
this will hopefully prevent so-called "zombie encounters" from popping up.

notes:

• this prevents submission by throwing a ServletException which is not very graceful at all and not a great user experience
• however, this is legacy submission and hopefully not long of this earth?
• plus, the case that triggers this seems to be pretty rare and might even be triggered by some browser issue (duplicate posting) that the user doesnt even see
• it was much easier than trying to do a very elegant message for this rare case

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 8.59%. Comparing base (c43934c) to head (c828d43).

Files with missing lines	Patch %	Lines
...c/main/java/org/ecocean/servlet/EncounterForm.java	0.00%	11 Missing ⚠️
src/main/java/org/ecocean/media/MediaAsset.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             seadragon   #1304      +/-   ##
==============================================
- Coverage         8.59%   8.59%   -0.01%     
  Complexity         941     941              
==============================================
  Files              623     623              
  Lines            68077   68088      +11     
  Branches         12578   12582       +4     
==============================================
  Hits              5853    5853              
- Misses           61618   61629      +11     
  Partials           606     606              

Flag	Coverage Δ
backend	8.59% <0.00%> (-0.01%)	⬇️
frontend	8.59% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.