Fix: skip Windows registry MIME entries with an invalid Content Type

[SAY-5]

On Windows, Crystal::System::MIME.load reads MIME types from the registry and calls MIME.register for each .<ext>\Content Type entry. If any entry holds an empty or malformed value, MIME.register raises ArgumentError ("Invalid media type: ...") which is unrescued, so a single bad registry entry aborts MIME initialization and crashes the first MIME.from_extension call.

The Unix loader already guards each source with a bare rescue (src/crystal/system/unix/mime.cr). This mirrors that: the per-entry register is wrapped so an invalid entry is skipped instead of taking down the whole load.

Fixes #17103.

The failing path is Windows-registry-specific, so I couldn't add a portable spec that exercises load directly. I confirmed the behavior of the guarded loop with the same call load makes (registering a batch where one entry has an empty Content Type): before the guard the ArgumentError aborts the loop, after it the bad entry is skipped and the remaining extensions register.

[HertzDevil]

While this is probably the right thing to do, did you encounter a corrupted registry naturally?

[Viktor-KN]

While this is probably the right thing to do, did you encounter a corrupted registry naturally?

I've reported this bug. Yes, registry corruption were encountered naturally on one of Windows 10 installations.