Fix NPE for FrameNodes that aren't NEW/FULL

All of the other types have a value of null for their list of
locals/stack elements.

Signed-off-by: Major <major@emulate.rs>

asm/src/main/java/dev/openrs2/asm/ClassNodeRemapper.kt

@@ -63,8 +63,8 @@ private fun Remapper.mapFrameType(type: Any): Any {
 private fun AbstractInsnNode.remap(remapper: Remapper) {
     when (this) {
         is FrameNode -> {
-            local = local.map(remapper::mapFrameType)
-            stack = stack.map(remapper::mapFrameType)
+            local = local?.map(remapper::mapFrameType)
+            stack = stack?.map(remapper::mapFrameType)
         }
         is FieldInsnNode -> {
             val originalOwner = owner