CORS middleware: better handling of Origin

[Ivshti]

no origin header should be treated as an empty origin header

otherwise, simple HTTP requests like ones made with curl will fail with 400 bad request

Pretty much any other framework/server treats the absence of an origin header the same as empty origin header

Description

Passing no origin header should be treated as an empty origin header

otherwise, simple HTTP requests like ones made with curl will fail with 400 bad request

Pretty much any other framework/server treats the absence of an origin header the same as empty origin header

Motivation and Context

Fixes simple HTTP requests, such as ones made with curl

How Has This Been Tested?

curl localhost:8000

curl -H 'Origin: something.com' localhost:8000

And to test the cases where it should be rejected, just set the origin to something and then see if any other origin will be rejected

Types of changes

• changed src/middleware.rs to apply the change

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.