The wheel `METADATA` parsing implemented in 1.4 missed the fact
that whitespace is significant and sometimes License is included
inline in the `METADATA` file itself.

This change ensures that we stop parsing the `METADATA` file only
on first completely empty line.

Fixes https://github.com/bazel-contrib/rules_python/issues/2796

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Co-authored-by: Ignas Anikevicius <240938+aignas@users.noreply.github.com>
(cherry picked from commit 1d69ad68d7959570acde61d8705f1f437c0691b0)