Sacado: Check for zero base in pow(Fad,Const)
Created by: etphipp
Most Sacado overloads of pow() check for a zero base, and return zero instead of evaluating the derivative even though in many situations this isn't technically correct (since the derivative is often not defined there). In PR #4380, I changed this behavior for the pow(Fad,Const) case, where I use a different formula. This was causing NaN's in Charon's Jacobian evaluation, so this commit restores the previous behavior (which again is technically not correct).