Fixing wrong user_ and community icon and banner urls.

- Fixes #1477

docker/dev/volume_mount.dockerfile

@@ -1,4 +1,6 @@
 # syntax=docker/dockerfile:experimental
+
+# Warning: this will not pick up migrations unless there are code changes
 FROM rust:1.50-buster as rust
 
 ENV HOME=/home/root

migrations/2021-03-04-040229_clean_icon_urls/down.sql

@@ -0,0 +1,3 @@
+-- This is a clean-up migration that cannot be undone,
+-- but Diesel requires a non-empty script so run a no-op.
+SELECT 1;

migrations/2021-03-04-040229_clean_icon_urls/up.sql

@@ -0,0 +1,5 @@
+-- If these are not urls, it will crash the server
+update user_ set avatar = NULL where avatar not like 'http%';
+update user_ set banner = NULL where banner not like 'http%';
+update community set icon = NULL where icon not like 'http%';
+update community set banner = NULL where banner not like 'http%';