WithZipFile should open a read only handle(or have the option to) about embedio

[rdeago]

Hello @jswigart, thanks for opening this issue.

Non-literally quoting myself from Slack:

The zip file is opened with FileAccess.ReadWrite and FileShare.Read (the default):
https://source.dot.net/#System.Private.CoreLib/src/libraries/System.Private.CoreLib/src/System/IO/FileStream.cs,120
We should use FileAccess.Read in the constructor call, as ReadWrite is not actualy needed.

There's no need for an option, as EmbedIO considers a Zip file an immutable file provider.

While we're on the subject, it wouldn't hurt to specify FileShare.Read explicitly too.

[rdeago]

This is the line to fix in version 3 (branch v3.x).

This is the line to fix in version 4 (branch master).

Any kind soul willing to submit a PR?