fix(agent): Add additonal NULL check

[zsistla]

No description provided.

[newrelic-php-agent-bot]

Test Suite	Status	Result
Multiverse	❌	6/8 passing
SOAK	✅	79/79 passing

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 77.87%. Comparing base (4bb2f2a) to head (f62d744).
Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
agent/lib_php_amqplib.c	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1046      +/-   ##
==========================================
+ Coverage   77.40%   77.87%   +0.47%     
==========================================
  Files         198      198              
  Lines       27715    27899     +184     
==========================================
+ Hits        21453    21727     +274     
+ Misses       6262     6172      -90     

Flag	Coverage Δ
agent-for-php-7.2	78.13% <0.00%> (+0.60%)	⬆️
agent-for-php-7.3	78.15% <0.00%> (+0.60%)	⬆️
agent-for-php-7.4	77.86% <0.00%> (+0.59%)	⬆️
agent-for-php-8.0	77.25% <0.00%> (+0.59%)	⬆️
agent-for-php-8.1	77.65% <0.00%> (+0.48%)	⬆️
agent-for-php-8.2	77.26% <0.00%> (+0.48%)	⬆️
agent-for-php-8.3	77.26% <0.00%> (+0.48%)	⬆️
agent-for-php-8.4	77.27% <0.00%> (+0.48%)	⬆️

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The base branch was changed.