bug symfony#28384 [VarDumper] First time dump() method call not working issue (me-shaon)

This PR was merged into the 4.2-dev branch.

Discussion
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[VarDumper] First time dump() method call not working issue

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#28370
| License       | MIT

Calling the `dump()` method for the first time is not producing any output. That's because, in the [latest change ](symfony/var-dumper@46434a6), the first call to the `dump` method is not calling the `$handler` at all. It's just setting the `$handler`.
In this PR, I've tried to fix this issue.

Commits
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b9681fe Fix symfony#28370: First time dump() method call not working issue

Author: nicolas-grekas

src/Symfony/Component/VarDumper/VarDumper.php

@@ -27,20 +27,21 @@ class VarDumper
 
     public static function dump($var)
     {
-        if (null !== self::$handler) {
-            return \call_user_func(self::$handler, $var);
+        if (null === self::$handler) {
+            $cloner = new VarCloner();
+
+            if (isset($_SERVER['VAR_DUMPER_FORMAT'])) {
+                $dumper = 'html' === $_SERVER['VAR_DUMPER_FORMAT'] ? new HtmlDumper() : new CliDumper();
+            } else {
+                $dumper = \in_array(\PHP_SAPI, array('cli', 'phpdbg')) ? new CliDumper() : new HtmlDumper();
+            }
+
+            self::$handler = function ($var) use ($cloner, $dumper) {
+                $dumper->dump($cloner->cloneVar($var));
+            };
         }
 
-        $cloner = new VarCloner();
-        if (isset($_SERVER['VAR_DUMPER_FORMAT'])) {
-            $dumper = 'html' === $_SERVER['VAR_DUMPER_FORMAT'] ? new HtmlDumper() : new CliDumper();
-        } else {
-            $dumper = \in_array(\PHP_SAPI, array('cli', 'phpdbg')) ? new CliDumper() : new HtmlDumper();
-        }
-
-        self::$handler = function ($var) use ($cloner, $dumper) {
-            $dumper->dump($cloner->cloneVar($var));
-        };
+        return \call_user_func(self::$handler, $var);
     }
 
     public static function setHandler(callable $callable = null)