For many families, the summer heat means backyard barbecues with plates filled to the brim with grilled burgers, hot dogs, potato salad and, of course, some fresh farm-picked corn-on-the-cob. But if you’re enjoying a side of corn with your dinner this month, make sure to savor it because it’s one ear that survived the brutal drought savaging local farmers. Jim Geoghegan, owner of Sunshine Farm in Sherborn, estimates he lost between 30 and 40 percent of all the crops he planted this year.