Fix hang in t5562, introduced in v2.21.0-rc1

The last-minute patch to replace /dev/zero with a Perl script snippet broke the Linux part of the CI builds on Azure Pipelines: it timed out. The culprit is the rb/no-dev-zero-in-test branch (see the build for this branch here [https://dev.azure.com/gitgitgadget/git/_build/results?buildId=1727]).

All of master, next, jch and pu are broken that way. You might see it in the commit status of the active branches
[https://github.com/gitgitgadget/git/branches/active].

Turns out that it is that particular Perl script snippet which for some reason hangs the build. If you kill it, t5562.15 succeeds, if you don't kill it, it will hang indefinitely (or until killed).

Sadly, despite my earnest attempts, I could not figure out why it hangs in those Linux agents (I could not reproduce that hang locally), or for that matter, why it does not hang in the Windows and macOS agents.

Let's avoid that hang. This patch fixes things on Azure Pipelines, and my hope is that it also fixes the hang on NonStop.

Johannes Schindelin (1):
tests: teach the test-tool to generate NUL bytes and use it

 Makefile                               |  1 +
 t/helper/test-genzeros.c               | 22 ++++++++++++++++++++++
 t/helper/test-tool.c                   |  1 +
 t/helper/test-tool.h                   |  1 +
 t/t5562-http-backend-content-length.sh |  2 +-
 t/test-lib-functions.sh                |  8 +-------
 6 files changed, 27 insertions(+), 8 deletions(-)
 create mode 100644 t/helper/test-genzeros.c

base-commit: 8989e1950a845ceeb186d490321a4f917ca4de47
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-126%2Fdscho%2Ffix-t5562-hang-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-126/dscho/fix-t5562-hang-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/126

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