By US standards, he was charged, then dismissed of the crime, and is now being tried a second time for the same crime. Almost nowhere else in the world has the strict double jeopardy laws the US has, but if we apply US standards, the charges and process are invalid many times over for many different reasons.
No - in the US, double jeopardy rights attach after voir dire, when the jury is empaneled and sworn in. There are plenty of times that charges are brought, amended, dropped, re-added, etc. before trial, and that's all irrelevant. There is nothing about Assange's case that remotely resembles double jeopardy.