Cambridge United took another step towards securing Sky Bet League One survival with this afternoon’s 1-1 draw at home against Charlton Athletic. The U’s headed into the clash at the Cledara Abbey Stadium with a five-point buffer to the relegation zone. And that gap has now grown to six after Garry Monk’s men battled back from being a goal down at half-time to salvage a share of the spoils. The opening exchanges were disrupted by two head injuries in quick succession for United’s James Gibbons and Zeno Ibsen Rossi. Both players were passed fit to continue after treatment, although a further st…