It's not necessarily failure to yield any more than it would be if you turned left in a gap between two oncoming cars. If you turn left before the oncoming car even starts moving, it's not failure to yield. For example, some dip who is too busy talking on his cell phone or texting to proceed in a timely manner when his light turns green. I'd for sure turn left in front of him and not cause him any inconvenience or lack of proper yield.