Avoid notice in case the header cannot be parsed.

Author: Edwin Westerhoud

src/class-tiny-compress.php

@@ -91,9 +91,9 @@ protected static function parse_headers($headers) {
         }
         $res = array();
         foreach ($headers as $header) {
-            list($key, $value) = explode(":", $header, 2);
-            if ($value) {
-                $res[$key] = trim($value);
+            $split = explode(":", $header, 2);
+            if (count($split) === 2) {
+                $res[$split[0]] = trim($split[1]);
             }
         }
         return $res;