OlmEncryption.encryptMessage(): devices can be null

[ShadowJonathan]

This came up while iterating #2137;

In OlmEncryption.encryptMessage, when iterating over devices per user, the function calls getStoredDevicesForUser, which can return null.

This does not throw an error, as any comparison operation with undefined is false.

matrix-js-sdk/src/crypto/algorithms/olm.ts

Line 123 in c1abab6

const devices = this.crypto.getStoredDevicesForUser(userId);

(Looking further into the code, I'm not sure if this is a real bug, or if this is (accidental) intended behavior.)