Allow indirect set in CappedMemoryCache

lib/private/cache/cappedmemorycache.php

@@ -64,8 +64,8 @@ class CappedMemoryCache implements ICache, \ArrayAccess {
 		return $this->hasKey($offset);
 	}
 
-	public function offsetGet($offset) {
-		return $this->get($offset);
+	public function &offsetGet($offset) {
+		return $this->cache[$offset];
 	}
 
 	public function offsetSet($offset, $value) {

tests/lib/cache/cappedmemorycache.php

@@ -64,4 +64,16 @@ class CappedMemoryCache extends \Test_Cache {
 		$this->assertFalse($this->instance->hasKey('2_value1'));
 		$this->assertFalse($this->instance->hasKey('3_value1'));
 	}
+
+	function testIndirectSet() {
+		$this->instance->set('array', []);
+
+		$this->instance['array'][] = 'foo';
+
+		$this->assertEquals(['foo'], $this->instance->get('array'));
+
+		$this->instance['array']['bar'] = 'qwerty';
+
+		$this->assertEquals(['foo', 'bar' => 'qwerty'], $this->instance->get('array'));
+	}
 }