Whole lotta QByteArray errors

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Just a heads up: I mentioned I run a cutting edge distro.
We use the QByteArray operator[] a lot in our xml module.
After a distro upgrade, I cannot run debug mode without getting thousands of errors
indicating problems with every call to that operator in the xml code.
Here is what my Qt help says:

Note: Before Qt 5.14 it was possible to use this operator to access a character at an out-of-bounds position in the byte array, and then assign to such a position, causing the byte array to be automatically resized. Furthermore, assigning a value to the returned QByteRef would cause a detach of the byte array, even if the byte array has been copied in the meanwhile (and the QByteRef kept alive while the copy was taken). These behaviors are deprecated, and will be changed in a future version of Qt.

Well, that has finally happened. I get thousands of errors when running in debug mode.
Therefore we need to fix that. I am thinking we need to replace usage of the [] operator
with simple append() or something.
I'll check it out and try to fix. Just warning y'all in case you get that too.

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Fixed in master now. Replaced [] usage with append() and clear() in xml module.
Tested OK opening and re-saving a complex song.
I've a feeling there may be other places that do that past-end [] thing.
Possibly the Deicsonze synth, maybe elsewhere.
Keep your eyes open for more errors and this type of usage, and avoid it in new code.
Thanks.