Don't reference update frames with VM_FRAME_MAGIC_DUMMY

Frames with VM_FRAME_MAGIC_DUMMY pushed by rb_vm_push_frame_fname have
allocated iseq, so we should not reference update it.

Author: peterzhu2118

vm.c

@@ -3367,20 +3367,22 @@ rb_execution_context_update(rb_execution_context_t *ec)
         }
 
         while (cfp != limit_cfp) {
-            const VALUE *ep = cfp->ep;
-            cfp->self = rb_gc_location(cfp->self);
-            cfp->iseq = (rb_iseq_t *)rb_gc_location((VALUE)cfp->iseq);
-            cfp->block_code = (void *)rb_gc_location((VALUE)cfp->block_code);
-
-            if (!VM_ENV_LOCAL_P(ep)) {
-                const VALUE *prev_ep = VM_ENV_PREV_EP(ep);
-                if (VM_ENV_FLAGS(prev_ep, VM_ENV_FLAG_ESCAPED)) {
-                    VM_FORCE_WRITE(&prev_ep[VM_ENV_DATA_INDEX_ENV], rb_gc_location(prev_ep[VM_ENV_DATA_INDEX_ENV]));
-                }
+            if (VM_FRAME_TYPE(cfp) != VM_FRAME_MAGIC_DUMMY) {
+                const VALUE *ep = cfp->ep;
+                cfp->self = rb_gc_location(cfp->self);
+                cfp->iseq = (rb_iseq_t *)rb_gc_location((VALUE)cfp->iseq);
+                cfp->block_code = (void *)rb_gc_location((VALUE)cfp->block_code);
+
+                if (!VM_ENV_LOCAL_P(ep)) {
+                    const VALUE *prev_ep = VM_ENV_PREV_EP(ep);
+                    if (VM_ENV_FLAGS(prev_ep, VM_ENV_FLAG_ESCAPED)) {
+                        VM_FORCE_WRITE(&prev_ep[VM_ENV_DATA_INDEX_ENV], rb_gc_location(prev_ep[VM_ENV_DATA_INDEX_ENV]));
+                    }
 
-                if (VM_ENV_FLAGS(ep, VM_ENV_FLAG_ESCAPED)) {
-                    VM_FORCE_WRITE(&ep[VM_ENV_DATA_INDEX_ENV], rb_gc_location(ep[VM_ENV_DATA_INDEX_ENV]));
-                    VM_FORCE_WRITE(&ep[VM_ENV_DATA_INDEX_ME_CREF], rb_gc_location(ep[VM_ENV_DATA_INDEX_ME_CREF]));
+                    if (VM_ENV_FLAGS(ep, VM_ENV_FLAG_ESCAPED)) {
+                        VM_FORCE_WRITE(&ep[VM_ENV_DATA_INDEX_ENV], rb_gc_location(ep[VM_ENV_DATA_INDEX_ENV]));
+                        VM_FORCE_WRITE(&ep[VM_ENV_DATA_INDEX_ME_CREF], rb_gc_location(ep[VM_ENV_DATA_INDEX_ME_CREF]));
+                    }
                 }
             }