make sure argsSet verifies string isn't empty too

[adelowo]

Else

• ./gitea admin create-user --name "dd" --email " " -password "" ( empty email and an empty password)

• ./gitea admin create-user --name oopsdd --email test@test.ddses -password "" (empty password) would work

• ./gitea admin create-user --name oopsdd --email test@test.ddses -password " "

• You cannot even enter an empty string via the ui since the input field has required

• If " " is accepted as an email in the cli, the user would end up updating in the settings page since the input field of the email is email and it would keep prompting to input a valid email address

[codecov-io]

Codecov Report

Merging #4980 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4980      +/-   ##
==========================================
- Coverage   37.57%   37.53%   -0.04%     
==========================================
  Files         322      322              
  Lines       47283    47283              
==========================================
- Hits        17766    17749      -17     
- Misses      26966    26983      +17     
  Partials     2551     2551

Impacted Files	Coverage Δ
models/repo_indexer.go	44.49% <0%> (-5.51%)	⬇️
modules/indexer/repo.go	63.35% <0%> (-5.35%)	⬇️
modules/process/manager.go	81.15% <0%> (+4.34%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4a685f8...a5057ec. Read the comment docs.

[zeripath]

Seems sensible. I wouldn't be surprised if people were abusing this to set empty email addresses during tests however, so it might need a highlight in the changelog, (and I should check I haven't done so myself.)