sched/irq: Avoid negative array index in irqchain_dispatch

IRQ_TO_NDX() may return a negative value when the IRQ number is invalid
or not mapped. Using this negative value directly as an array index for
g_irqvector causes undefined behavior and potential memory corruption.

This patch adds a bounds check to ensure ndx is non-negative before
accessing the g_irqvector array, returning the error code if invalid.

Signed-off-by: pangzhen1 <pangzhen1@xiaomi.com>

sched/irq/irq_chain.c

@@ -80,6 +80,12 @@ static int irqchain_dispatch(int irq, FAR void *context, FAR void *arg)
   int ndx = IRQ_TO_NDX(irq);
   int ret = 0;
 
+  if (ndx < 0)
+    {
+      ret = ndx;
+    }
+  else
+    {
       curr = g_irqvector[ndx].arg;
       while (curr != NULL)
         {
@@ -87,6 +93,7 @@ static int irqchain_dispatch(int irq, FAR void *context, FAR void *arg)
           curr = curr->next;
           ret |= prev->handler(irq, context, prev->arg);
         }
+    }
 
   return ret;
 }