Make sure we don't trash our userinfo after we get it and before we s…

…end it.

findOccupiedUserSlot can end up overwriting some of the buffers that
emberAfPluginDoorLockGetUser uses, so we need to make sure we call
findOccupiedUserSlot before emberAfPluginDoorLockGetUser (or after we are done
using the output from emberAfPluginDoorLockGetUser).

src/app/clusters/door-lock-server/door-lock-server.cpp

@@ -453,6 +453,20 @@ void DoorLockServer::getUserCommandHandler(chip::app::CommandHandler * commandOb
         return;
     }
 
+    Commands::GetUserResponse::Type response;
+
+    // appclusters, 5.2.4.36.1: We need to add next occupied user after userIndex if any.
+    //
+    // We want to do this before we call emberAfPluginDoorLockGetUser, because this will
+    // make its own emberAfPluginDoorLockGetUser calls, and a
+    // EmberAfPluginDoorLockUserInfo might be pointing into some application-static
+    // buffers (for its credentials and whatnot).
+    uint16_t nextAvailableUserIndex = 0;
+    if (findOccupiedUserSlot(commandPath.mEndpointId, static_cast<uint16_t>(userIndex + 1), nextAvailableUserIndex))
+    {
+        response.nextUserIndex.SetNonNull(nextAvailableUserIndex);
+    }
+
     EmberAfPluginDoorLockUserInfo user;
     if (!emberAfPluginDoorLockGetUser(commandPath.mEndpointId, userIndex, user))
     {
@@ -461,7 +475,6 @@ void DoorLockServer::getUserCommandHandler(chip::app::CommandHandler * commandOb
         return;
     }
 
-    Commands::GetUserResponse::Type response;
     response.userIndex = userIndex;
 
     // appclusters, 5.2.4.36: we should not set user-specific fields to non-null if the user status is set to Available