templater: fix shortest() to evaluate int argument and handle error

templater: fix pad() to evaluate int argument and handle error

templater: drop redundant type conversion when evaluating integer argument A function argument may be an integer. In this case, it isn't necessary to convert a value to string and back to integer. Because an argument may be an arbitrary object (e.g. date tuple), TypeError should be caught as well.

templater: factor out function that evaluates argument as integer We have more bare int()s that may raise ValueError or TypeError. This function will be used to fix them.