LibACPI: Fix a crash on filtered opcode at root

When an opcode would get filtered at root it would try to get the
opcode value to print the error message, which is absent on the root
frame.

Userland/Libraries/LibACPI/Interpreter.cpp

@@ -326,6 +326,9 @@ ErrorOr<IterationDecision> Interpreter::cycle(TableStream& stream)
         auto opcode = TRY(stream.read_opcode());
         if (!top_opcode_frame.filter_opcode_for_next_operand(opcode)) {
             DEBUG_LOG("Failure!");
+            if (m_opcode_frames.size() == 1)
+                INTERPRETER_ERROR("Filtered opcode!", EINVAL, "Argument opcode {} filtered at root!", opcode);
+
             INTERPRETER_ERROR("Filtered opcode!", EINVAL, "Argument opcode {} filtered by opcode {}!", opcode, top_opcode_frame.opcode());
         }