minor symfony#61471 [HttpFoundation] Don’t check suffix on empty MIME type (MatTheCat)

This PR was squashed before being merged into the 7.4 branch.

Discussion
----------

[HttpFoundation] Don’t check suffix on empty MIME type

| Q             | A
| ------------- | ---
| Branch?       | 7.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | N/A
| License       | MIT

Fix tests from symfony#61267 (remaining failures unrelated).

Commits
-------

3816617 [HttpFoundation] Don’t check suffix on empty MIME type

Author: nicolas-grekas

src/Symfony/Component/HttpFoundation/Request.php

@@ -1259,8 +1259,8 @@ public function getFormat(?string $mimeType, bool $subtypeFallback = false): ?st
             }
         }
 
-        if (!$canonicalMimeType) {
-            $canonicalMimeType = $mimeType;
+        if (!$canonicalMimeType ??= $mimeType) {
+            return null;
         }
 
         if (str_starts_with($canonicalMimeType, 'application/') && str_contains($canonicalMimeType, '+')) {
@@ -1964,8 +1964,6 @@ protected static function initializeFormats(): void
     }
 
     /**
-     * Structured MIME suffix fallback formats
-     *
      * This mapping is used when no exact MIME match is found in $formats.
      * It enables handling of types like application/soap+xml → 'xml'.
      *

src/Symfony/Component/HttpFoundation/Tests/RequestTest.php

@@ -538,9 +538,7 @@ public static function getFormatToMimeTypeMapProvider()
         ];
     }
 
-    /**
-     * @dataProvider getFormatWithSubtypeFallbackProvider
-     */
+    #[DataProvider('getFormatWithSubtypeFallbackProvider')]
     public function testGetFormatFromMimeTypeWithSubtypeFallback($expectedFormat, $mimeTypes)
     {
         $request = new Request();