[PhpUnitBridge] Fix undefined index when output of "composer show" cannot be parsed

src/Symfony/Bridge/PhpUnit/bin/simple-phpunit

@@ -106,6 +106,11 @@ if (!file_exists("$PHPUNIT_DIR/phpunit-$PHPUNIT_VERSION/phpunit") || md5_file(__
         }
     }
 
+    $info += [
+        'versions' => [],
+        'requires' => ['php' => '*'],
+    ];
+
     if (1 === \count($info['versions'])) {
         $passthruOrFail("$COMPOSER create-project --ignore-platform-reqs --no-install --prefer-dist --no-scripts --no-plugins --no-progress --ansi -s dev phpunit/phpunit phpunit-$PHPUNIT_VERSION \"$PHPUNIT_VERSION.*\"");
     } else {