inspector: Allows reentry when paused

This change allows reentering the message dispatch loop when the Node is
paused. This is necessary when the pause happened as a result of the
message sent by a debug frontend, such as evaluating a function with a
breakpoint inside.

Fixes: https://github.com/nodejs/node/issues/13320
PR-URL: https://github.com/nodejs/node/pull/13350


Reviewed-By: James M Snell <jasnell@gmail.com>