Prevent upload of empty submission corrections

[Splines]

This is a temporary fix for #513 by preventing empty file uploads.

• During correction upload
• During bulk correction upload
• Not checked: size during submission uploads by users

Where in the codebase

To test it in the UI, search for the string":type option"in the codebase. Once you've found the comment, set the size to 0 manually by adding

data.metadata.size = 0

above. Then, go ahead and upload any file in respective view. You should see a warning and not be able to complete upload.

Backend

Note: this is only a UI fix, not checking this on the backend, users could still upload empty files via POST. We might still want to ship this to prevent basic errors in the frontend during upload and to maybe find the reason for #513.
We are also checking for the minimum file size in the backend. To test it, change

if data.metadata.size == 0

to

if false

Then, users are able to upload the empty file in the frontend, but when they click on "Save", it will fail (with the same error message), as the backend validation fails.

Dummy file

Use the following dummy file as an empty file to test with: empty-file.pdf

[codecov]

Codecov Report

Merging #552 (4af005a) into mampf-next (3289e75) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           mampf-next     #552      +/-   ##
==============================================
+ Coverage       66.49%   66.51%   +0.02%     
==============================================
  Files             311      311              
  Lines            9417     9423       +6     
==============================================
+ Hits             6262     6268       +6     
  Misses           3155     3155              

Files	Coverage Δ
app/uploaders/correction_uploader.rb	100.00% <100.00%> (ø)
app/uploaders/submission_uploader.rb	100.00% <100.00%> (ø)

[fosterfarrell9]

I did some testing in my local setup, and it seems to be working nicely.