fix: try and prevent crash from missing file when thumbnailing

[vinitkumar]

Description

Fix crash in filer performing easy-thumbnails thumb-nailing when for some reason the image is not present.

An earlier fix #1379 was done, but it didn't take care of all edge cases, but this one does and gracefully rescues the error and at the same time provides a fallback.

Related resources

Checklist

• [x] I have opened this pull request against master
• [x] I have added or modified the tests when changing logic
• [x] I have followed the conventional commits guidelines to add meaningful information into the changelog
• [x] I have read the contribution guidelines and I have joined #workgroup-pr-review on Slack to find a “pr review buddy” who is going to review my pull request.

[codecov[bot]]

Codecov Report

Merging #1388 (99f71a5) into master (71d16ca) will decrease coverage by 0.18%. The diff coverage is 30.76%.

@@            Coverage Diff             @@
##           master    #1388      +/-   ##
==========================================
- Coverage   73.98%   73.80%   -0.18%     
==========================================
  Files          75       75              
  Lines        3436     3443       +7     
  Branches      552      552              
==========================================
- Hits         2542     2541       -1     
- Misses        722      731       +9     
+ Partials      172      171       -1     

Impacted Files	Coverage Δ
filer/templatetags/filer_admin_tags.py	84.11% <25.00%> (-6.89%)	:arrow_down:
filer/__init__.py	100.00% <100.00%> (ø)