Improve conversion between typed arrays

Co-authored-by: Fedor Indutny <79877362+indutny-signal@users.noreply.github.com>

ts/Crypto.ts

@@ -35,7 +35,12 @@ export type EncryptedAttachment = {
 
 // Generate a number between zero and 16383
 export function generateRegistrationId(): number {
-  const id = new Uint16Array(getRandomBytes(2))[0];
+  const bytes = getRandomBytes(2);
+  const id = new Uint16Array(
+    bytes.buffer,
+    bytes.byteOffset,
+    bytes.byteLength / 2
+  )[0];
 
   // eslint-disable-next-line no-bitwise
   return id & 0x3fff;

ts/test-electron/Crypto_test.ts

@@ -165,12 +165,18 @@ describe('Crypto', () => {
 
   describe('generateRegistrationId', () => {
     it('generates an integer between 0 and 16383 (inclusive)', () => {
+      let max = 0;
       for (let i = 0; i < 100; i += 1) {
         const id = generateRegistrationId();
         assert.isAtLeast(id, 0);
         assert.isAtMost(id, 16383);
         assert(Number.isInteger(id));
+
+        max = Math.max(max, id);
       }
+
+      // Probability of this being false is ~ 10^{-181}
+      assert.isAtLeast(max, 0x100);
     });
   });