Merge branch '5.4' into 6.3

* 5.4:
  [Translation] Fix `TranslationNodeVisitor` with constant domain
  [Messenger] [AMQP] Throw exception on `nack` callback
  [Validator] revise Latvian translations
  [ErrorHandler] Fix `RecursiveDirectoryIterator` exception with wrong composer autoload
  [HttpFoundation] Request without content-type or content-length header should result in null values, not empty strings
  [Cache] Fix possible infinite loop in `CachePoolPass`
  [Mime] Fix undefined array key 0 when empty sender
  [Console] Allow '0' as a $shortcut in InputOption.php
  fix multi-byte code area to convert
  [Validator] Make it explicit when English translation differs from its resource name

Author: nicolas-grekas

ErrorEnhancer/ClassNotFoundErrorEnhancer.php

@@ -107,7 +107,8 @@ private function getClassCandidates(string $class): array
 
     private function findClassInPath(string $path, string $class, string $prefix): array
     {
-        if (!$path = realpath($path.'/'.strtr($prefix, '\\_', '//')) ?: realpath($path.'/'.\dirname(strtr($prefix, '\\_', '//'))) ?: realpath($path)) {
+        $path = realpath($path.'/'.strtr($prefix, '\\_', '//')) ?: realpath($path.'/'.\dirname(strtr($prefix, '\\_', '//'))) ?: realpath($path);
+        if (!$path || !is_dir($path)) {
             return [];
         }