ConsoleBuf: Fix test case when running under Windows Terminal

Brad Kingrequested to merge
brad.king/kwsys:ConsoleBuf-windows-terminal into master

Since commit 4967ccc0 (ConsoleBuf: Fix output for strings that contain null byte, 2016-11-09) our test case writes a NUL byte to the console. The behavior of Windows Terminal differs from Windows Console Host (conhost.exe). Detect which of these is in use at runtime and adjust our expected result accordingly.

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