Fix access to QByteArray/QString outside the valid range. (#537)

Fix access to QByteArray/QString outside the valid range. (#537)

With Qt 5.15, and likely 5.14, the following warnings were generated during
testo:
Using QByteRef with an index pointing outside the valid range of a QByteArray. The corresponding behavior is deprecated, and will be changed in a future version of Qt.
Using QCharRef with an index pointing outside the valid range of a QString. The corresponding behavior is deprecated, and will be changed in a future version of Qt.
Note this requires Qt to be compiled for debug.

These warnings can be debugged by running testo with
"export QT_FATAL_WARNINGS=1" to generate core dumps.

I suspect the appending of null terminators in ggv_bin is unecessary,
i.e. I beleive QByteArray::resize() in ggv_bin_read_bytes will take
care of this.  Never the less I slavishly kept adding them just to make
certain.