[Bugfix] Targeting when attack.def = ''

[kyleady]

Issue

When creating a power, It is possible to select the defense for the attack as no defense.

This functions without issue when nothing is targeted. However, when at least one token is targeted an exception is thrown, leaving the Attack button in the Power Chat Card in the disabled state. A new Power Chat Card needs to be generated and all tokens untargeted before trying again. The error is

dice.js:206 Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'value')
[Detected 1 package: system:dnd4e]
    at performD20RollAndCreateMessage (dice.js:206)
    at Object.callback (dice.js:90)
    at Dialog.submit (foundry.js:44156)
    at Dialog._onClickButton (foundry.js:44119)
    at HTMLButtonElement.dispatch (jquery.min.js:2)
    at HTMLButtonElement.v.handle (jquery.min.js:2)

Fix

The solution offered in this PR

• Conditionally skips adding the DND4EBETA.VS text if the attack isn't against any defense.
• Sets targDefVal to undefined when the targeted creature does not have that defense, using optional chaining.
• Skips calculating hitState if targDefVal === undefined.

Example: Attacking four targeted tokens when Item4e.data.data.attack.def = ''.

I have tested that the hitState is still calculated when the value of a target's defense is equal to 0 for a valid defense. It would only not display the hitState if a creature somehow had undefined for a valid defense.