Make MVM_args_proc_cleanup idempotent

So that even if we do somehow end up calling it twice somehow, we'll
never risk a double free. It's rare that we end up with so many named
arguments that we need this buffer anyway, so the zeroing is no real
loss.

src/core/args.h

@@ -68,9 +68,11 @@ MVM_STATIC_INLINE void MVM_args_proc_setup(MVMThreadContext *tc, MVMArgProcConte
 
 /* Clean up an arguments processing context. */
 MVM_STATIC_INLINE void MVM_args_proc_cleanup(MVMThreadContext *tc, MVMArgProcContext *ctx) {
-    if (ctx->named_used_size > 64)
+    if (ctx->named_used_size > 64) {
         MVM_fixed_size_free(tc, tc->instance->fsa, ctx->named_used_size,
             ctx->named_used.byte_array);
+        ctx->named_used_size = 0;
+    }
 }
 
 /* Argument processing context handling. */

src/core/frame.c

@@ -128,8 +128,7 @@ static void instrumentation_level_barrier(MVMThreadContext *tc, MVMStaticFrame *
  * part of a continuation that was taken but never invoked, we should check
  * things normally cleaned up on return don't need cleaning up also. */
 void MVM_frame_destroy(MVMThreadContext *tc, MVMFrame *frame) {
-    if (frame->work)
-        MVM_args_proc_cleanup(tc, &frame->params);
+    MVM_args_proc_cleanup(tc, &frame->params);
     if (frame->env && !MVM_FRAME_IS_ON_CALLSTACK(tc, frame))
         MVM_fixed_size_free(tc, tc->instance->fsa, frame->allocd_env, frame->env);
     if (frame->extra) {