An over discharged battery CAN safely be charged, but the damage caused can limit the max charge the pack can take (so charging over it's diminished limit is like over-charging) and cause the voltage to drop sharply under load.
Like all batteries, the state of yours is prone to circumstance. It could very well be fine, or it could catch fire next time you charge it at 1C to full capacity
Honestly when it comes to LiPo's, you can get a high quality pack for $9-$40, so why bother taking the risk? lol