read-installed silently ignores errors from readdir-scoped-modules.readdir

[ddfisher]

Prior to 1.0.1, readdir-scoped-modules would throw EMFILE errors when reading large node_modules folders. Because read-installed assumes a readdir error simply implies an empty directory, this caused some installed modules to not be reported and lead to npm/npm#6506 (see this comment in particular). read-installed should either not suppress errors here or only suppress explicitly expected error types.