Deliver even when an error raised in the block argument

[aki77]

Goal

I would also like to be notified if there is an error in the block argument of the notify method.
This is because the more important the error handling, the more complex the contents of the block argument, and the more likely it is that an error will occur.

[johnkiely1]

Hey @aki77,
Thanks for the PR, we will look to review as soon as priorities allow.

[imjoehaines]

Thanks for the PR @aki77, this is a really useful fix!

I'll merge this in #664 where I've made a change to log a warning instead of adding metadata. This is what we do in other places where we rescue errors from user-supplied functions, 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

[aki77]

Thanks!