drop the "NOT NULL" constraint from the "port" column when converting the DB

pyweb/mumble/conversionsql/mysql/01-schema-prepare-mumble.sql

@@ -4,6 +4,8 @@ ALTER TABLE `mumble_mumble`
         ADD `server_id` integer FIRST;
 ALTER TABLE `mumble_mumble`
         ADD `display` varchar(200) AFTER `name`;
+ALTER TABLE `mumble_mumble`
+	MODIFY `port` integer NULL;
 COMMIT;
 
 BEGIN;

pyweb/mumble/conversionsql/pgsql/01-schema-prepare-mumble.sql

@@ -3,6 +3,8 @@ ALTER TABLE "mumble_mumble"
         ADD "server_id" integer NULL REFERENCES "mumble_mumbleserver" ("id") DEFERRABLE INITIALLY DEFERRED;
 ALTER TABLE "mumble_mumble"
         ADD "display" varchar(200);
+ALTER TABLE "mumble_mumble"
+	ALTER "port" DROP NOT NULL;
 
 CREATE INDEX "mumble_mumble_server_id" ON "mumble_mumble" ("server_id");
 

pyweb/mumble/conversionsql/sqlite/01-schema-mumble.sql

@@ -4,7 +4,7 @@ CREATE TABLE "mumble_mumble_new" (
     "name" varchar(200) NOT NULL,
     "srvid" integer NOT NULL,
     "addr" varchar(200) NOT NULL,
-    "port" integer NOT NULL,
+    "port" integer,
     "display" varchar(200) NOT NULL,
     UNIQUE ("server_id", "srvid")
 );