Fix edge case where summary_message is not assigned in dbt debug

[dbeatty10]

resolves #9436

Problem

When running dbt debug in certain circumstances, I get a python stack trace that ends in the following:

UnboundLocalError: local variable 'summary_message' referenced before assignment

Solution

Two parts to the solution:

1. Add a default summary_message
2. Consider it an error if no profile names are found

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2f2e0ce) 87.85% compared to head (ade867b) 87.85%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9437      +/-   ##
==========================================
- Coverage   87.85%   87.85%   -0.01%     
==========================================
  Files         150      150              
  Lines       21915    21918       +3     
==========================================
+ Hits        19253    19255       +2     
- Misses       2662     2663       +1     

Flag	Coverage Δ
integration	85.30% <66.66%> (-0.01%)	⬇️
unit	62.56% <100.00%> (+0.17%)	⬆️

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