Fix source span on CR characters.

[isoos]

Fixes #1014.

[sigurdm]

Is the source span in the linked issue not created somewhere else (related to license detection)?
Could this be fixed in source_span instead?

Do we need a test of this?

[isoos]

Is the source span in the linked issue not created somewhere else (related to license detection)?
Could this be fixed in source_span instead?

We could wait for dart-lang/source_span#79 to be fixed, but I think we can also mitigate this by this PR, as we already have the try-catch block with a comment that CRs are causing trouble. Once the package:source_span issue is fixed, we can simplify this code. I'll add a TODO to note this.

Do we need a test of this?

Shall I add an end2end test case for it?

[sigurdm]

Shall I add an end2end test case for it?

Or perhaps just a unit-test. The end2end tests are a bit heavy.

[sigurdm]

LGTM