Correct migrations to not re-remove fields.

evennia/scripts/migrations/0011_remove_scriptdb_db_player.py

@@ -2,7 +2,17 @@
 # Generated by Django 1.11.2 on 2017-07-06 20:41
 from __future__ import unicode_literals
 
-from django.db import migrations
+from django.db import migrations, OperationalError, connection
+
+
+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):
@@ -11,9 +21,14 @@ class Migration(migrations.Migration):
         ('scripts', '0010_auto_20170705_1736'),
     ]
 
-    operations = [
-        migrations.RemoveField(
-            model_name='scriptdb',
-            name='db_account',
-        ),
-    ]
+    db_cursor = connection.cursor()
+
+    if not _table_exists(db_cursor, 'scripts_scriptdb_db_player'):
+        operations = []
+    else:
+        operations = [
+            migrations.RemoveField(
+                model_name='scriptdb',
+                name='db_player',
+            ),
+        ]