bug symfony#29057 [HttpFoundation] replace any preexisting Content-Type headers (nicolas-grekas)

This PR was merged into the 2.8 branch.

Discussion
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[HttpFoundation] replace any preexisting Content-Type headers

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#21204
| License       | MIT
| Doc PR        | -

Commits
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de2ce58 [HttpFoundation] replace any preexisting Content-Type headers

Author: nicolas-grekas

src/Symfony/Component/HttpFoundation/Response.php

@@ -344,8 +344,9 @@ public function sendHeaders()
 
         // headers
         foreach ($this->headers->allPreserveCase() as $name => $values) {
+            $replace = 0 === strcasecmp($name, 'Content-Type');
             foreach ($values as $value) {
-                header($name.': '.$value, false, $this->statusCode);
+                header($name.': '.$value, $replace, $this->statusCode);
             }
         }