Decide whether or not Quill will handle the copy event THEN preventDefault.

[conlanpatrek]

Resolves #4572

The issue was an order of operations. Whenever the clipboard module captures a copy event it calls preventDefault() on it before it actually decides to do anything with the event.

This PR just moves the call to preventDefault() after the clipboard module decides to handle it.

In the case where the user selects the contents before, including, and after the quill root, the onCopyCapture handler doesn't get called, because some parent node handles the copy event.

In the case where the user selects only text within the quill root, this.quill.selection.getRange() is able to return a valid range.

However in cases where selection goes off the end of the quill root this.quill.selection.getRange() returns null, resulting in a copy handler that prevents default AND doesn't handle the copy.