wxCharBuffer.extend(len) bugfix

[troelsk]

wxCharBuffer.extend(len) makes room for the zero terminator.
But it does not set it to 0 as it should (as the corresponding ctor does), so you end up with a non-terminated string.

This bug exists in both trunk and wx28 branch!

[troelsk]

Trunk

[troelsk]

2.8 branch

[VZ]

(In [70417]) Ensure wxCharTypeBuffer data is NUL-terminated after extend() call.

As wxCharTypeBuffer ctor taking the length NUL-terminates the buffer, it may
be expected that extend() does the same but it did not. Do add the NUL at the
end for consistency, even though it's not really needed for the existing code
using extend() in wxWidgets itself.

Closes #13885.

[troelsk]

2.8 branch

[troelsk]

Remove redundant termination code, in trunk

[troelsk]

Added patch removing unnecessary termination code in trunk

[VZ]

(In [73141]) Don't unnecessarily NUL-terminate wxCharBuffer contents.

wxCharBuffer already initializes the last byte of the buffer it allocates to 0
so there is no need to do it explicitly.

Also don't allocate an extra byte, wxCharBuffer already adds one to the length
passed to it for the trailing NUL.

See #13885.