Crash more nicely when the VM isn't fully set up

If we crash but the VM isn't fully alive, we can get an infinite loop.

vm_dump.c

@@ -1062,6 +1062,7 @@ rb_vm_bugreport(const void *ctx)
 		    LIMITED_NAME_LENGTH(name), RSTRING_PTR(name));
 	    fprintf(stderr, "\n");
         }
+        if (vm->loaded_features) {
             fprintf(stderr, "* Loaded features:\n\n");
             for (i=0; i<RARRAY_LEN(vm->loaded_features); i++) {
                 name = RARRAY_AREF(vm->loaded_features, i);
@@ -1092,6 +1093,7 @@ rb_vm_bugreport(const void *ctx)
                             (void *)name);
                 }
             }
+        }
 	fprintf(stderr, "\n");
     }