Write the debug log only when debugging is enabled

The debug log isn't automatically cleaned so don't write to it when
debugging is disabled and thus nobody is aware that debug output might
be generated.

inc/infoutils.php

@@ -304,6 +304,9 @@ function dbg($msg,$hidden=false){
  */
 function dbglog($msg,$header=''){
     global $conf;
+    // The debug log isn't automatically cleaned thus only write it when
+    // debugging has been enabled by the user.
+    if($conf['allowdebug'] !== 1) return;
     if(is_object($msg) || is_array($msg)){
         $msg = print_r($msg,true);
     }