client: Don't crash when outdated plugins are trying to load

runelite-client/src/main/java/net/runelite/client/plugins/ExternalPluginManager.java

@@ -503,6 +503,12 @@ public class ExternalPluginManager
 					{
 						//noinspection unchecked
 						plugininst = instantiate(scannedPlugins, (Class<Plugin>) pluginClazz, init, initConfig);
+
+						if (plugininst == null)
+						{
+							return;
+						}
+
 						scannedPlugins.add(plugininst);
 					}
 					catch (PluginInstantiationException e)
@@ -654,6 +660,11 @@ public class ExternalPluginManager
 		{
 			throw new PluginInstantiationException(ex);
 		}
+		catch (NoClassDefFoundError ex)
+		{
+			log.error("Plugin {} is outdated", clazz.getSimpleName());
+			return null;
+		}
 
 		log.debug("Loaded plugin {}", clazz.getSimpleName());
 		return plugin;
@@ -712,6 +723,8 @@ public class ExternalPluginManager
 	private List<Plugin> loadPlugin(String pluginId)
 	{
 		List<Plugin> scannedPlugins = new ArrayList<>();
+		try
+		{
 			List<Plugin> extensions = externalPluginManager.getExtensions(Plugin.class, pluginId);
 			for (Plugin plugin : extensions)
 			{
@@ -746,6 +759,11 @@ public class ExternalPluginManager
 
 				scannedPlugins.add(plugin);
 			}
+		}
+		catch (NoClassDefFoundError ex)
+		{
+			log.error("plugin {} is outdated", pluginId);
+		}
 
 		return scannedPlugins;
 	}