Fix spam filtering when the score is negative

dovecot/sieve/before.sieve

@@ -9,14 +9,15 @@ require "relational";
 require "comparator-i;ascii-numeric";
 require "vnd.dovecot.extdata";
 
-if string :is "${extdata.spam_enabled}" "1" {
+if allof (string :is "${extdata.spam_enabled}" "1",
-  if header :matches "X-Spam-Status" "* score=*" {
+          not header :matches "X-Spam-Status" "* score=-*",
+          header :matches "X-Spam-Status" "* score=*")
+{
   if string :value "ge" :comparator "i;ascii-numeric" "${2}" "${extdata.spam_threshold}" {
     setflag "\\seen";
     fileinto :create "Junk";
     stop;
   }
-  }
 }
 
 if string :is "${extdata.reply_enabled}" "1" {