Fix notice when handling c3 error before C3_CODECOVERAGE_MEDIATE_STORAGE is defined

Author: marcovtwout

c3.php

@@ -38,9 +38,13 @@
 if (!function_exists('__c3_error')) {
     function __c3_error($message)
     {
-        $errorLogFile = defined('C3_CODECOVERAGE_ERROR_LOG_FILE') ?
-            C3_CODECOVERAGE_ERROR_LOG_FILE :
-            C3_CODECOVERAGE_MEDIATE_STORAGE . DIRECTORY_SEPARATOR . 'error.txt';
+        if (defined('C3_CODECOVERAGE_ERROR_LOG_FILE')) {
+            $errorLogFile = C3_CODECOVERAGE_ERROR_LOG_FILE;
+        } elseif (defined('C3_CODECOVERAGE_MEDIATE_STORAGE')) {
+            $errorLogFile = C3_CODECOVERAGE_MEDIATE_STORAGE . DIRECTORY_SEPARATOR . 'error.txt';
+        } else {
+            $errorLogFile = null;
+        }
         if (is_writable($errorLogFile)) {
             file_put_contents($errorLogFile, $message);
         } else {