Merge branch '4.4' into 5.4

* 4.4:
  [HttpKernel] lock when writting profiles
  Using identical comparison for path validation
  [Mime] Fix email rendering when having inlined parts that are not related to the content
  [HttpFoundation] move flushing outside of Response::closeOutputBuffers
  [FrameworkBundle] Do not throw when describing a factory definition
  Fix checking result of DateTime::getLastErrors

Author: nicolas-grekas

Constraints/DateTimeValidator.php

@@ -42,7 +42,7 @@ public function validate($value, Constraint $constraint)
 
         \DateTime::createFromFormat($constraint->format, $value);
 
-        $errors = \DateTime::getLastErrors();
+        $errors = \DateTime::getLastErrors() ?: ['error_count' => 0, 'warnings' => []];
 
         if (0 < $errors['error_count']) {
             $this->context->buildViolation($constraint->message)