Checks to prevent re-queuing plugins

includes/RestApi/PluginsController.php

@@ -322,6 +322,15 @@ public function set_site_features( \WP_REST_Request $request ) {
 
 		foreach ( $plugins as $plugin => $decision ) {
 			if ( $decision ) {
+				// If the Plugin exists and is activated
+				if ( PluginInstaller::exists( $plugin, $decision ) )
+					continue;
+
+				// If the Plugin is already in queue
+				$position_in_queue = PluginInstallTaskManager::status( $plugin );
+				if ( false !== $position_in_queue )
+					continue;
+
 				PluginInstallTaskManager::add_to_queue(
 					new PluginInstallTask(
 						$plugin,