Merge branch '6.4' into 7.0

* 6.4:
  [Scheduler] Throw an exception when no dispatcher has been passed to a Schedule
  [Mime] Fix TextPart using an unknown File
  Fix autoload configs to avoid warnings when building optimized autoloaders

Part/TextPart.php

@@ -123,7 +123,11 @@ public function getName(): ?string
     public function getBody(): string
     {
         if ($this->body instanceof File) {
-            return file_get_contents($this->body->getPath());
+            if (false === $ret = @file_get_contents($this->body->getPath())) {
+                throw new InvalidArgumentException(error_get_last()['message']);
+            }
+
+            return $ret;
         }
 
         if (null === $this->seekable) {

Tests/Part/TextPartTest.php

@@ -12,6 +12,7 @@
 namespace Symfony\Component\Mime\Tests\Part;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\Mime\Exception\InvalidArgumentException;
 use Symfony\Component\Mime\Header\Headers;
 use Symfony\Component\Mime\Header\ParameterizedHeader;
 use Symfony\Component\Mime\Header\UnstructuredHeader;
@@ -55,6 +56,16 @@ public function testConstructorWithFile()
         $this->assertSame('content', implode('', iterator_to_array($p->bodyToIterable())));
     }
 
+    public function testConstructorWithUnknownFile()
+    {
+        $p = new TextPart(new File(\dirname(__DIR__).'/Fixtures/unknown.txt'));
+
+        // Exception should be thrown only when the body is accessed
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessageMatches('{Failed to open stream}');
+        $p->getBody();
+    }
+
     public function testConstructorWithNonStringOrResource()
     {
         $this->expectException(\TypeError::class);