Catch error when unable to send DM

[christolis]

Fixes #797. I was unable to test this, but I think this might be a solid solution.

[CLAassistant]

All committers have signed the CLA.

[SquidXTV]

you can maybe instead supply null for the success Consumer.
not sure if its better/cleaner code then though

success - The success callback that will be called at a convenient time for the API. (can be null to use default)

https://docs.jda.wiki/net/dv8tion/jda/api/requests/RestAction.html#queue(java.util.function.Consumer,java.util.function.Consumer)

[surajkumar]

Maybe we can have the users name in the log message? Though not too important. Maybe the log message itself can be improved

[SquidXTV]

Maybe we can have the users name in the log message? Though not too important

wont it be in the exception?