Add a sanity check for comm migration

evennia/comms/migrations/0013_auto_20170705_1726.py

@@ -2,7 +2,17 @@
 # Generated by Django 1.11.2 on 2017-07-05 17:26
 from __future__ import unicode_literals
 
-from django.db import migrations, models
+from django.db import migrations, models, connection
+from django.db import OperationalError
+
+def _table_exists(db_cursor, tablename):
+    "Returns bool if table exists or not"
+    sql_check_exists = "SELECT * from %s;" % tablename
+    try:
+        db_cursor.execute(sql_check_exists)
+        return True
+    except OperationalError:
+        return False
 
 
 class Migration(migrations.Migration):
@@ -12,6 +22,13 @@ class Migration(migrations.Migration):
         ('comms', '0012_merge_20170617_2017'),
     ]
 
+    db_cursor = connection.cursor()
+
+    if not _table_exists(db_cursor, 'comms_msg_db_hide_from_players'):
+        # OBS - this is run BEFORE migrations are run!
+        # not a migration of an existing database
+        operations = []
+    else:
         operations = [
             migrations.AddField(
                 model_name='channeldb',