Return early when no finding maps are built

What does this MR do and why?

This fixes #435853 (closed) by optimizing the vulnerability creation process of CVS. Instead of raising an error and tracking the error in Sentry, we exit early from the service's #execute method. The previous error was noisy and unactionable, which ultimately detracted from actionable and valid errors. We already track individual errors related to build issues, so we will still be able to track edge cases encountered during the finding build stage.

Fixes #435853 (closed)

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I tested this out by adding a rspec test that simulates an empty finding map creation. Since the spec passes in a [] array for the affected components, the #map method produces [] for the finding_maps result (the scenario we occasionally see in Sentry).