Issue #, if available:

LoggingTest.cpp:90:18: error: null destination pointer [-Werror=format-truncation=]
         vsnprintf(outputBuff.GetUnderlyingData(), requiredLength, formatStr, args);
         ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Some gcc versions seem to not like our Aws::Array container.
Description of changes:
Add explicit check for pointer to be allocated.
Check all that applies:

• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

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