A true missing clad layer coin would have been rejected on most vending machines, but it doesn't look like a missing clad layer, just environmental damage as discussed above. If you had tried it in a Coke machine it most likely would have taken the coin with no problem.
Your coin should weigh in the area of 5.67 grams, maybe a little less because of corrosion. Clad quarters that are missing a layer weigh around 4.67 grams, as the clad layer weighs about 1 gram.
"Shine, shine, a Roosevelt dime
All the way to Baltimore and running out of time" - Tom Waits 'Clap Hands'