fix(request): anticipate operations with no inputs

[Tieske]

If no inputs were available, this would throw hard errors.

[github-actions]

Luacheck Report

3 tests   - 36   0 ✅ ± 0   0s ⏱️ ±0s
1 suites ± 0   0 💤 ± 0 
1 files   ± 0   3 ❌  - 36 

For more details on these failures, see this check.

Results for commit a47ea82. ± Comparison against base commit f6a4468.

This pull request removes 39 and adds 3 tests. Note that renamed tests count towards both.

spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:1
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:10
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:11
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:12
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:13
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:14
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:15
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:16
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:17
spec/03-credentials/04-RemoteCredentials_spec.lua ‑ spec/03-credentials/04-RemoteCredentials_spec.lua:18
…

src/resty/aws/init.lua ‑ src/resty/aws/init.lua:1
src/resty/aws/request/build.lua ‑ src/resty/aws/request/build.lua:1
src/resty/aws/request/build.lua ‑ src/resty/aws/request/build.lua:2

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