What if the ray is perpendicular to the normal vector and the line is ON the plane? What would the value of t be in this case?
In that case, t does not have a well defined value, because any value of t would result in a point on the plane. If you really needed to handle a case like this, you would probably have to detect the situation and use another algorithm for a ray-line intersection on the bounding edge of the face that is contained by the plane. However, I you would generally not need to worry about this because due to randomly generated rays, extremely specific cases like that will statistically never happen.