ZP-1386 Update mimedecode include. Released under the Affero GNU General...

ZP-1386 Update mimedecode include. Released under the Affero GNU General Public License (AGPL) version 3.

src/include/mimeDecode.php

@@ -538,7 +538,7 @@ class Mail_mimeDecode
 
                 $hdr_name = substr($value, 0, $pos = strpos($value, ':'));
                 $hdr_value = substr($value, $pos+1);
-                if($hdr_value[0] == ' ') {
+                if(strlen($hdr_value) && $hdr_value[0] == ' ') {
                     $hdr_value = substr($hdr_value, 1);
                 }