bug #4242 Fix CoreExtension::captureOutput (nicolas-grekas)

This PR was merged into the 3.x branch.

Discussion
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Fix CoreExtension::captureOutput

Fix #4146

I forgot these lines in #4216

Commits
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7ba6866 Fix CoreExtension::captureOutput

src/Extension/CoreExtension.php

@@ -1888,30 +1888,22 @@ public static function checkArrowInSandbox(Environment $env, $arrow, $thing, $ty
      */
     public static function captureOutput(iterable $body): string
     {
-        $output = '';
         $level = ob_get_level();
         ob_start();
 
         try {
             foreach ($body as $data) {
-                if (ob_get_length()) {
-                    $output .= ob_get_clean();
-                    ob_start();
-                }
-
-                $output .= $data;
-            }
-
-            if (ob_get_length()) {
-                $output .= ob_get_clean();
+                echo $data;
             }
-        } finally {
+        } catch (\Throwable $e) {
             while (ob_get_level() > $level) {
                 ob_end_clean();
             }
+
+            throw $e;
         }
 
-        return $output;
+        return ob_get_clean();
     }
 
     /**