RescuedExceptionInterceptor: Handle empty configuration

Previously, it could happen that `Sentry.configuration` was `nil`.
In this case, calling `rails` would produce a `NoMethodError`.
We fix this issue by using safe navigation.

Furthermore, this commit ensures we use a reasonable default
in case the configuration couldn't be loaded. Since the config
`report_rescued_exceptions` defaults to `true`, we assume
this value here, too.
 
Fixes #2386

sentry-rails/lib/sentry/rails/rescued_exception_interceptor.rb

@@ -19,7 +19,10 @@ def call(env)
       end
 
       def report_rescued_exceptions?
-        Sentry.configuration.rails.report_rescued_exceptions
+        report_rescued_exceptions = Sentry.configuration&.rails&.report_rescued_exceptions
+        return report_rescued_exceptions unless report_rescued_exceptions.nil?
+
+        true
       end
     end
   end