Previously, BeanCurrentlyInCreationFailureAnalyzer would return
a FailureAnalysis for any BeanCurrentlyInCreationException even if
it could not determine where the cycle begins. This could lead to an
inaccurate diagram of the cycle being output.

This commit updates BeanCurrentlyInCreationFailureAnalyzer so that
it abandons its analysis and returns null if it is unable to determine
where the cycle begins.

Closes gh-8164