[BUGFIX] Fix t3x download with empty conflicts

[mbrodala]

The "conflicts" of an extension may be an empty string instead of an empty array which must be taken into account. This fixes the following error:

[ErrorException]
  array_keys() expects parameter 1 to be array, string given

[mbrodala]

The full exception trace as seen with -vvv:

Exception trace:
 () at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/Downloader/T3xDownloader.php:379
 Composer\Util\ErrorHandler::handle() at n/a:n/a
 array_keys() at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/Downloader/T3xDownloader.php:379
 TYPO3\CMS\Composer\Installer\Downloader\T3xDownloader::dependencyToString() at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/Downloader/T3xDownloader.php:335
 TYPO3\CMS\Composer\Installer\Downloader\T3xDownloader->fixEmConf() at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/Downloader/T3xDownloader.php:264
 TYPO3\CMS\Composer\Installer\Downloader\T3xDownloader->constructEmConf() at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/Downloader/T3xDownloader.php:249
 TYPO3\CMS\Composer\Installer\Downloader\T3xDownloader->writeEmConf() at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/Downloader/T3xDownloader.php:70
 TYPO3\CMS\Composer\Installer\Downloader\T3xDownloader->extract() at phar:///usr/local/bin/composer/src/Composer/Downloader/ArchiveDownloader.php:44
 Composer\Downloader\ArchiveDownloader->download() at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/Downloader/T3xDownloader.php:50
 TYPO3\CMS\Composer\Installer\Downloader\T3xDownloader->download() at phar:///usr/local/bin/composer/src/Composer/Downloader/DownloadManager.php:199
 Composer\Downloader\DownloadManager->download() at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/ExtensionInstaller.php:191
 TYPO3\CMS\Composer\Installer\ExtensionInstaller->installCode() at /tmp/test/vendor/typo3/cms-composer-installers/Classes/TYPO3/CMS/Composer/Installer/ExtensionInstaller.php:123
 TYPO3\CMS\Composer\Installer\ExtensionInstaller->install() at phar:///usr/local/bin/composer/src/Composer/Installer/InstallationManager.php:152
 Composer\Installer\InstallationManager->install() at phar:///usr/local/bin/composer/src/Composer/Installer/InstallationManager.php:139
 Composer\Installer\InstallationManager->execute() at phar:///usr/local/bin/composer/src/Composer/Installer.php:604
 Composer\Installer->doInstall() at phar:///usr/local/bin/composer/src/Composer/Installer.php:232
 Composer\Installer->run() at phar:///usr/local/bin/composer/src/Composer/Command/InstallCommand.php:134
 Composer\Command\InstallCommand->execute() at phar:///usr/local/bin/composer/vendor/symfony/console/Command/Command.php:259
 Symfony\Component\Console\Command\Command->run() at phar:///usr/local/bin/composer/vendor/symfony/console/Application.php:841
 Symfony\Component\Console\Application->doRunCommand() at phar:///usr/local/bin/composer/vendor/symfony/console/Application.php:192
 Symfony\Component\Console\Application->doRun() at phar:///usr/local/bin/composer/src/Composer/Console/Application.php:167
 Composer\Console\Application->doRun() at phar:///usr/local/bin/composer/vendor/symfony/console/Application.php:123
 Symfony\Component\Console\Application->run() at phar:///usr/local/bin/composer/src/Composer/Console/Application.php:98
 Composer\Console\Application->run() at phar:///usr/local/bin/composer/bin/composer:43
 require() at /usr/local/bin/composer:25

[sascha-egerer]

+1