Fix compatibility issue with LibSharedMedia

It appears LibSharedMedia does not always initialize the media lists from
the media tables. To fix this we make sure the media lists match the
media tables when the table already exists upon addon initialization.

src/LibFreeMedia.lua

@@ -42,6 +42,7 @@ local DEFAULT_MEDIA_TABLE = {
     }
 }
 
+-- Build default media lists from the default media table
 local function MakeDefaultList()
     local lists = {}
     for kind, media in pairs(DEFAULT_MEDIA_TABLE) do
@@ -66,6 +67,18 @@ do
         libsm = LibStub:NewLibrary("LibSharedMedia-3.0", 0)
         libsm.MediaTable = DEFAULT_MEDIA_TABLE
         libsm.MediaList = DEFAULT_MEDIA_LIST
+    else
+        -- Ensure the lists match the tables if we didn't create them
+        for kind, media in pairs(libsm.MediaTable) do
+            if libsm.MediaList[kind] == nil then
+                local mediaList = {}
+                for identifier, _ in pairs(media) do
+                    table.insert(mediaList, identifier)
+                end
+                table.sort(mediaList)
+                libsm.MediaList[kind] = mediaList
+            end
+        end
     end
 
     ---@type table<string, table<string, any>> 
@@ -94,7 +107,7 @@ local function RegisterOne(kind, identifier, data)
     end
 
     media[identifier] = data
-    table.insert(lib.mediaList[kind], identifier)
+    table.insert(mediaList, identifier)
     return true
 end