QML should emit warnings when doing invalid conversions

If QML has to do an "implicit conversion" in order to set a property's value, it should really check that the result of the conversion is legitimate, otherwise it should emit a warning. Only warnings about assigning "undefined" seem to be emitted.

Object {
   property color c: "foobar" // "foobar" is not a valid color; should warn
   property int i: NaN // not representable, should warn
   property int i2: Infinity // ditto
   property int i3: 3.14 // heck, I'd even claim that *this* should warn.
}

Here's a more complex example:

Object {
   property int p: otherObject.doesNotExist + 1
   Object { id: otherObject }
}

This does not emit a warning (although it should) on accessing the non existant property because of QTBUG-85069.

If one omits the +1, one gets a warning: "unable to assign undefined to int". Makes sense.

But with the +1, undefined+number => NaN, and then the warning disappears. Instead, it should emit ANOTHER warning: you can't set NaN to an integer.