win: Explain the CreateFile() client-side pipe-opening loop
win: Explain the CreateFile() client-side pipe-opening loop

The bug and linked code review has more of the history, but we’ve been
tempted to remove the loop outright a couple of times already before
realizing that it serves an important purpose. Hopefully this comment
will protect our future selves from going on the same fool’s errand.

BUG=crashpad:75
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/1427643010 .

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