Fix: Safely parse value in template

[Xowap]

Problem

When clearing the value or providing an invalid value in the input, the template goes through some warnings [and fatal errors if you're using the debug mode].

Solution

Parsing is done using a computed property that will always have a correct value (defaulting to today's date) if the parsed value is not correct.

As a side effect, there is a performance bonus as the value is only parsed once.