wasm: Allow badvalue in the get_tracked spec

A hook that violates its contract makes the whole call return the bare
atom, which the edoc describes and the tests pin, but the spec promised
a list. Say so until that return becomes an exception.

Author: bettio

libs/avm_emscripten/src/emscripten.erl

@@ -396,7 +396,7 @@ run_script_tracked(_Script) ->
 %% `{error, badkey}' / `{error, badvalue}' tuples
 -spec get_tracked
     (_TrackedObjects :: [tracked_object(), ...], key) -> [non_neg_integer()];
-    (_TrackedObjects :: [tracked_object(), ...], value) -> [get_tracked_result()].
+    (_TrackedObjects :: [tracked_object(), ...], value) -> [get_tracked_result()] | badvalue.
 get_tracked(_TrackedObjects, _Type) ->
     erlang:nif_error(undefined).