For number type, use a user-defined validation text instead of "Please enter a valid value."

[Piskvor]

The JS library always uses a hardcoded error text: "Please enter a valid value." if a type="number" field is misfilled. It should only fall back to the hardcoded text if no error message has been defined.

• bugfix
• issues: none
• documentation: not needed
• BC break: no