Correct error in how additional global and non-persistent groups are added,...

Correct error in how additional global and non-persistent groups are added, which corrupted the arrays holding those groups.

In 868c0a8c, I blindly copied two missing functions from another object caching plugin, not paying enough attention to how that plugin managed the data versus how this plugin does. As a result, the arrays of groups had some entries keyed by the group, others were unkeyed and the value represented the group.

object-cache.php

@@ -1071,8 +1071,7 @@ class WP_Object_Cache {
 	function add_global_groups( $groups ) {
 		$groups = (array) $groups;
 
-		$groups = array_fill_keys( $groups, true );
-		$this->global_groups = array_merge( $this->global_groups, $groups );
+		$this->global_groups = array_unique( array_merge( $this->global_groups, $groups ) );
 	}
 
 	/**
@@ -1083,7 +1082,6 @@ class WP_Object_Cache {
 	function add_non_persistent_groups( $groups ) {
 		$groups = (array) $groups;
 
-		$groups = array_fill_keys( $groups, true );
-		$this->no_redis_groups = array_merge( $this->no_redis_groups, $groups );
+		$this->no_redis_groups = array_unique( array_merge( $this->no_redis_groups, $groups ) );
 	}
 }