Remove unnecessary conditional

As of 0b81a48, `ROBJECT_IVPTR` will
always return a value, so we don't need to test whether or not we got
one.  T_OBJECTs always come to life as embedded objects, so they will
return an ivptr, and when they become "unembedded" they will have an
ivptr at that point too

gc.c

@@ -5702,16 +5702,14 @@ gc_mark_children(rb_objspace_t *objspace, VALUE obj)
         {
             const VALUE * const ptr = ROBJECT_IVPTR(obj);
 
-            if (ptr) {
-                uint32_t i, len = ROBJECT_NUMIV(obj);
-                for (i  = 0; i < len; i++) {
-                    gc_mark(objspace, ptr[i]);
-                }
+            uint32_t i, len = ROBJECT_NUMIV(obj);
+            for (i  = 0; i < len; i++) {
+                gc_mark(objspace, ptr[i]);
+            }
 
-                if (LIKELY(during_gc) &&
+            if (LIKELY(during_gc) &&
                     ROBJ_TRANSIENT_P(obj)) {
-                    rb_transient_heap_mark(obj, ptr);
-                }
+                rb_transient_heap_mark(obj, ptr);
             }
         }
 	break;