[Macintosh] QLineEdit doesn't handle Delete with modifiers correctly

A QLineEdit doesn't handle (modifier)+Delete key combinations correctly.

To reproduce:

1) Paste some text with words into a QLineEdit (say, "Paste some text with words")

2) Click somewhere in a space in the middle of the text.

3) Hold down the Option key and press Delete. That is 

QKeySequence::DeleteStartOfWord. It deletes the word before the cursor, as expected.

4) Keep doing that until the cursor is at the start of the text. Now it deletes the character to the right of the cursor. *** That's a bug ***

Another:

1) Paste some text with words into a QLineEdit (say, "Paste some text with words")

2) Click somewhere in a space in the middle of the text.

3) Hold down the Cmd key and press Delete. That is 

QKeySequence::DeleteCompleteLine. It deletes everything to the start of the line of text, as expected.

4) Do it again; it deletes the character to the right of the cursor. *** That's a bug ***

The first of these is caused by this code in QWidgetLineControl.cpp, in QWidgetLineControl::processKeyEvent():
(I'm trying to paste code; how do I do that?)
{{
  else if (event == QKeySequence::DeleteStartOfWord) {
if (!isReadOnly())

}
}}

This code tries to set the cursor on the text, but doesn't make sure that it is possible to do correctly. If the cursor is at the start of the line, it should not try to do anything.

The other example is more complicated because it does not match a pre-existing QKeySequence. But the same is true- no test is done to make sure the cursor is in a proper position before calling del().

A less important problem is that Control and Cmd are confused- they both do the same thing, which is not expected on a Macintosh. I understand why that is, but it is unexpected.