[Code Inspection] It's not always possible to get the code snippet

[busykai]

Some linting providers (most notably JSHint) may report negative line number Indicating general provide problem. For example, it may happen when there's an internal code inspection provider (e.g. configuration file is broken). Currently, it causes a crash in code inspection:

Uncaught TypeError: Cannot read property 'length' of undefined CodeInspection.js:312

While there's a protection against NaN (recently added), there's no check for negative numbers so that code snippet could be retrieved from the current editor.

[dangoor]

Medium priority to @peterflynn to take a look at the fix and see if @busykai should submit a pull request for that

[dangoor]

Oops #6442 is the pull request.