minor #40584 [PasswordHasher] The $algorithms array is only used when…

… $algorithm is set (rosier)

This PR was merged into the 5.3-dev branch.

Discussion
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[PasswordHasher] The $algorithms array is only used when $algorithm is set

| Q             | A
| ------------- | ---
| Branch?       | 5.x
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Small tweak

Commits
-------

0144d0a The $algorithms array is only used when $algorithm is set

src/Symfony/Component/PasswordHasher/Hasher/NativePasswordHasher.php

@@ -49,17 +49,17 @@ public function __construct(int $opsLimit = null, int $memLimit = null, int $cos
             throw new \InvalidArgumentException('$cost must be in the range of 4-31.');
         }
 
-        $algorithms = [1 => \PASSWORD_BCRYPT, '2y' => \PASSWORD_BCRYPT];
+        if (null !== $algorithm) {
+            $algorithms = [1 => \PASSWORD_BCRYPT, '2y' => \PASSWORD_BCRYPT];
 
-        if (\defined('PASSWORD_ARGON2I')) {
-            $algorithms[2] = $algorithms['argon2i'] = (string) \PASSWORD_ARGON2I;
-        }
+            if (\defined('PASSWORD_ARGON2I')) {
+                $algorithms[2] = $algorithms['argon2i'] = (string) \PASSWORD_ARGON2I;
+            }
 
-        if (\defined('PASSWORD_ARGON2ID')) {
-            $algorithms[3] = $algorithms['argon2id'] = (string) \PASSWORD_ARGON2ID;
-        }
+            if (\defined('PASSWORD_ARGON2ID')) {
+                $algorithms[3] = $algorithms['argon2id'] = (string) \PASSWORD_ARGON2ID;
+            }
 
-        if (null !== $algorithm) {
             $this->algorithm = $algorithms[$algorithm] ?? $algorithm;
         }