Could not write error to log file

[petrabarus]

While debugging for this issue Codeception/Codeception#4871, I keep getting message Could not write error to log file.
When I traced the cause, it's from here.

c3/c3.php

Lines 36 to 43 in c7348bb

	$errorLogFile = defined('C3_CODECOVERAGE_ERROR_LOG_FILE') ?
	C3_CODECOVERAGE_ERROR_LOG_FILE :
	C3_CODECOVERAGE_MEDIATE_STORAGE . DIRECTORY_SEPARATOR . 'error.txt';
	if (is_writable($errorLogFile)) {
	file_put_contents($errorLogFile, $message);
	} else {
	$message = "Could not write error to log file ($errorLogFile), original message: $message";
	}

Apparently the c3tmp directory is always emptied by __c3_clear() when the test is executed.

c3/c3.php

Lines 288 to 291 in c7348bb

	if ($route === 'clear') {
	__c3_clear();
	return __c3_exit();
	}

This cause problem because is_writable returns true if the file exists and is writable.

http://php.net/manual/en/function.is-writable.php