inner input width to 100% if calculation is NaN

Some usecases pre-render widget before attaching to DOM ( e.g., Backbone-Marionette). In these cases inner input width calculation yields NaN because jquery's dimension methods yields NaN. The end result is the width being defaulted to minWidth and long placeholders get chopped off (recurrence of closed issue #37).

For these cases, this fix defaults the width to 100% instead of minWidth. This fix also has the benefit of setting width only once instead of twice as in the previous implementation.