bpo-30790: fix proxy works uncorrectly if registry value end with a semicolon

[Cordius]

The function proxy_bypass_registry will return 1 if registry value end
with a semicolon because a NULL string will be contained in the variable
proxyOverride while using proxyOverride.split(';'). And therefore, our
proxy will never work correctly.

[csabella]

@Cordius, please take a look at the comments on the bug tracker issue.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[iritkatriel]

As was mentioned on the issue, a change like this requires a unit test that reproduces the bug being fixed.

[bedevere-bot]

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