Allow nullable ReferenceCounted objects to be passed to use

Signed-off-by: Graham <gpe@openrs2.org>

buffer/src/main/kotlin/org/openrs2/buffer/ReferenceCountedExtensions.kt

@@ -2,10 +2,10 @@ package org.openrs2.buffer
 
 import io.netty.util.ReferenceCounted
 
-public inline fun <T : ReferenceCounted, R> T.use(block: (T) -> R): R {
+public inline fun <T : ReferenceCounted?, R> T.use(block: (T) -> R): R {
     try {
         return block(this)
     } finally {
-        release()
+        this?.release()
     }
 }