check RET in _join

ChangeLog

@@ -7,6 +7,7 @@
 	(chx_sched): Add an argument for race avoidance.
 	(chopstx_intr_wait): Fix the race condition.
 	(chopstx_cond_broadcast): Fix initial value.
+	(chopstx_join): Check RET.
 
 	* board/board-olimex-stm32-h103.h (NEUG_ADC_SETTING2_*): Add.
 

chopstx.c

@@ -1131,7 +1131,8 @@ chopstx_join (chopstx_t thd, void **ret)
     }
 
   tp->state = THREAD_FINISHED;
-  *ret = (void *)tp->tc.reg[0];
+  if (ret)
+    *ret = (void *)tp->tc.reg[0];
   asm volatile ("cpsie   i" : : : "memory");
 }