Review fixes: the derived key is wiped also when a key is damaged, each tidy-up step after a removal on its own

- The key derived from the passphrase is wiped on every path, also when the key or nonce turns out damaged
- After a removal the pending flag and the cached index are tidied up independently; a failing log cannot stop the removal event
- Tests: a short salt or nonce gives the damaged-key error

tests/Unit/Crypto/KeyRingTest.php

@@ -30,6 +30,19 @@ class KeyRingTest extends TestCase {
 		KeyRing::unwrapAny($wrapped, 'right');
 	}
 
+	public function testAShortSaltOrNonceIsADamagedKey(): void {
+		foreach (['salt', 'nonce'] as $part) {
+			$wrapped = KeyRing::generate()->wrap('right');
+			$wrapped[$part] = base64_encode('short');
+			try {
+				KeyRing::unwrapAny($wrapped, 'right');
+				$this->fail("a short $part was accepted");
+			} catch (CryptoException $e) {
+				$this->assertStringContainsString('Damaged key file', $e->getMessage(), $part);
+			}
+		}
+	}
+
 	public function testBlobIdsAreKeyed(): void {
 		$this->assertNotSame(KeyRing::generate()->blobId('same'), KeyRing::generate()->blobId('same'));
 		$k = KeyRing::generate();