Fix error with return statement in for-loop body

This error occurred when a return statement was in for-loop body. After
parsing loop body, "body_" was assigned NULL as the return value,
causing the compiler to failed in correctly connect "inc_" and
"cond_start" basic blocks.

This error can be analyzed by examining the CFG.dot file.

src/parser.c

@@ -2608,6 +2608,8 @@ basic_block_t *read_body_statement(block_t *parent, basic_block_t *bb)
         if (body_) {
             bb_connect(body_, inc_, NEXT);
             bb_connect(inc_, cond_start, NEXT);
+        } else if (inc_->insn_list.head) {
+            bb_connect(inc_, cond_start, NEXT);
         } else {
             /* TODO: Release dangling inc basic block */
         }