fix out-of-bound access on compiling empty blocks.

src/codegen.c

@@ -511,8 +511,9 @@ for_body(codegen_scope *s, node *tree)
   }
   codegen(s, tree->cdr->cdr->car, VAL);
   pop();
+  if (s->pc > 0) {
     c = s->iseq[s->pc-1];
-  if (GET_OPCODE(c) != OP_RETURN || GETARG_B(c) != OP_R_NORMAL || s->pc == s->lastlabel) {
+    if (GET_OPCODE(c) != OP_RETURN || GETARG_B(c) != OP_R_NORMAL || s->pc == s->lastlabel)
       genop_peep(s, MKOP_AB(OP_RETURN, cursp(), OP_R_NORMAL), NOVAL);
   }
   loop_pop(s, NOVAL);
@@ -593,6 +594,7 @@ lambda_body(codegen_scope *s, node *tree, int blk)
   }
   codegen(s, tree->cdr->car, VAL);
   pop();
+  if (s->pc > 0) {
     c = s->iseq[s->pc-1];
     if (GET_OPCODE(c) != OP_RETURN || GETARG_B(c) != OP_R_NORMAL || s->pc == s->lastlabel) {
       if (s->nregs == 0) {
@@ -603,6 +605,7 @@ lambda_body(codegen_scope *s, node *tree, int blk)
         genop_peep(s, MKOP_AB(OP_RETURN, cursp(), OP_R_NORMAL), NOVAL);
       }
     }
+  }
   if (blk) {
     loop_pop(s, NOVAL);
   }