fix issue 15136 - If we want toStringz to be fully correct, it needs …

[aG0aep6G]

…to stop checking for '\0'

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	15136	normal	If we want toStringz to be fully correct, it needs to stop checking for '\0'

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#7806"

[schveiguy]

LGTM. One thing to think about, if there is already a null character on a string value (within the bounds), then reallocation isn't going to do anything.

[PetarKirov]

Some related discussion regarding this optimization:
https://forum.dlang.org/post/ildzweoczmwvflodfadk@forum.dlang.org

[RazvanN7]

This seems to be failing on CircleCi