Add error message for XLIFF file load (#1627)

[anvit]

Throwing an exception when Symfony runs into issues when loading XLIFF files. This will help with catching broken XML files due to translation errors. Without any error handling, this would lead Symfony to use an empty array as the array of translations when it is unable to read XML files, and would make it delete all existing translations for such a file.

[anvit]

This is one potential way to safeguard against this problem. Another could be to add a warning/exception in vendor/symfony/lib/i18n/sfMessageSource.class.php for scenarios where loadData doesn't return an array.

atom/vendor/symfony/lib/i18n/sfMessageSource.class.php

Lines 193 to 201 in d996e1c

	$data = &$this->loadData($source);
	if (is_array($data))
	{
	$this->messages[$variant] = $data;
	if ($this->cache)
	{
	$this->cache->set($variant.':'.$this->culture, serialize($data));
	}
	}

Decided to go with adding it here since generating the exception right when we're having an issue with loading the XLIFF file seemed like the more logical behaviour, but let me know if there's a better way, or a reason not to do this.

[mcantelon]

One suggestion but looks good otherwise!

[mcantelon]

Using sprinf to assemble the error message might be cleaner, but otherwise looks solid.

[anvit]

Done!

[mcantelon]

Looks good to me!