Turn inline_end annotated pointless gotos into no_ops

We can't remove them completely as that causes weird deopt issues. But turning
them into no_ops should give almost the same benefits without the cost.

src/spesh/optimize.c

@@ -2422,9 +2422,15 @@ static void eliminate_pointless_gotos(MVMThreadContext *tc, MVMSpeshGraph *g) {
                 && last_ins->info->opcode == MVM_OP_goto
                 && last_ins->operands[0].ins_bb == cur_bb->linear_next
                 && ! any_deopt_annotations(last_ins->annotations)
-                && (! any_inline_end_annotations(last_ins->annotations))
-            )
-                MVM_spesh_manipulate_delete_ins(tc, g, cur_bb, last_ins);
+            ) {
+                if (
+                    any_inline_end_annotations(last_ins->annotations)
+                    || last_ins == cur_bb->first_ins // May not throw away the only instruction
+                )
+                    last_ins->info = MVM_op_get_op(MVM_OP_no_op);
+                else
+                    MVM_spesh_manipulate_delete_ins(tc, g, cur_bb, last_ins);
+            }
         }
         cur_bb = cur_bb->linear_next;
     }