Profilers - do not write when there's no summary

[carmocca]

What does this PR do?

Avoids PassThroughProfiler printing empty logs whenever describe is called. This happens because its summary fn returns an empty string. This PR avoids logging in that case.

No need for CHANGELOG update as this bug is unreleased.

Before submitting

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[codecov]

Codecov Report

Merging #6681 (7b2a13c) into master (0ea8f39) will decrease coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #6681    +/-   ##
=======================================
- Coverage      91%     87%    -4%     
=======================================
  Files         192     192            
  Lines       12266   12301    +35     
=======================================
- Hits        11178   10677   -501     
- Misses       1088    1624   +536     

[tchaton]

LGTM !