minor #18932 Improve memory efficiency (Dword123)

This PR was merged into the 2.7 branch.

Discussion
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Improve memory efficiency

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

This avoids concatenating `$message` and `PHP_EOL` (if necessary) as a new value, greatly improving memory efficiency for large `$message`s.

Commits
-------

c1df9f2 Improve memory efficiency

src/Symfony/Component/Console/Output/StreamOutput.php

@@ -70,7 +70,7 @@ public function getStream()
      */
     protected function doWrite($message, $newline)
     {
-        if (false === @fwrite($this->stream, $message.($newline ? PHP_EOL : ''))) {
+        if (false === @fwrite($this->stream, $message) || ($newline && (false === @fwrite($this->stream, PHP_EOL)))) {
             // should never happen
             throw new \RuntimeException('Unable to write output.');
         }