Deliver even when an error raised in the block argument

[imjoehaines]

Goal

This is #660 with next merged and the implementation tweaked to log a message instead of adding metadata, so it's consistent with how we handle errors in other places — e.g. in on_error callbacks:

bugsnag-ruby/lib/bugsnag/on_error_callbacks.rb

Lines 13 to 18 in 98b73dc

	begin
	should_continue = callback.call(report)
	rescue StandardError => e
	Bugsnag.configuration.warn("Error occurred in on_error callback: '#{e}'")
	Bugsnag.configuration.warn("on_error callback stacktrace: #{e.backtrace.inspect}")
	end