Partially filled time validation error is not cleared if input is cleared

[jelhan]

#279 had introduced a validation error if a time input is only partially filled (e.g. hour but no minutes). This validation error is not removed if user clears the input using keyboard or the clear button provided by UI.

This only affects Chrome as that one is the only browser that shows the validation error in the first place. See #279 for details.

Steps to reproduce:

• Create a poll until you reach the time input.
• Enter a partially time (e.g. only hour).
• Leave focus of that input and see validation error.
• Clear the input.

The validation error should be cleared but it's still visible. It's only cleared on change but as a partially filled time does not that the value, there isn't any change triggered...