cli/debug: fix OTELErrorHandler logging messages if there's no error

[thaJeztah]

• relates to [BUG] Building with bake hangs indefinitely compose#12998

I noticed this in a ticket in the compose issue tracker; with debug logging enabled, the OTEL error-logger may be logging even if there's no error;

DEBU[0000] Executing bake with args: [bake --file - --progress rawjson --metadata-file /tmp/compose-build-metadataFile-1203980021.json --allow fs.read=/home/user/dev/project --allow fs.read=/home/user/dev/project --allow fs.read=/home/user/dev/project/nginx --allow fs.read=/home/user/dev/project]
TRAC[0000] Plugin server listening on @docker_cli_d8df486f78df3b7357995be71bf0cef6
DEBU[0005] otel error                                    error="<nil>"
^CTRAC[0055] Closing plugin server
TRAC[0055] Closing plugin server
DEBU[0055] otel error                                    error="<nil>"
DEBU[0055] otel error                                    error="<nil>"

Update the error-handler to not log if there's no error.

- What I did

- How I did it

- How to verify it

- Human readable description for the release notes

Fix stray "otel error" logs being printed if debug logging is enabled.

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 54.82%. Comparing base (74a896f) to head (4ea6fbf).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6160      +/-   ##
==========================================
- Coverage   54.83%   54.82%   -0.01%     
==========================================
  Files         364      364              
  Lines       30467    30470       +3     
==========================================
  Hits        16706    16706              
- Misses      12786    12789       +3     
  Partials      975      975              

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