Errors are sometimes thrown with "warn" option #113

This is a:

• Bug Report

Which concerns:

• flow-runtime

What is the current behaviour?

With the warn: true option, some invariants may still throw errors, for example this one: https://github.com/codemix/flow-runtime/blob/13e72fcc064bb6060c9ba49c58be3efe2f20ff40/packages/flow-runtime/src/flowTypes/%24ShapeType.js#L64

What is the expected behaviour?

Runtime should log a warning.

Which package versions are you using?

flow-runtime: 0.12

warn function (https://github.com/codemix/flow-runtime/blob/8bfdd7461f34d74bcb60247bf9b4b5644ab9e3b0/packages/flow-runtime/src/TypeContext.js#L1004) runs validation, but doesn't protect it from thrown errors