fix: 没设置串口回调时会调用空指针的bug， close #I4HREO

platform/drivers/uart/wm_uart.c

@@ -621,7 +621,7 @@ ATTRIBUTE_ISR void UART0_IRQHandler(void)
         fifos = port->regs->UR_FIFOS;
         uart_handle_cts_change(port, fifos & UFS_CST_STS);
     }
-    if (intr_src & UIS_RX_FIFO_TIMEOUT)
+    if (port->rx_callback != NULL && intr_src & UIS_RX_FIFO_TIMEOUT)
     {
         port->rx_callback(0, (void*)((int)port->priv_data+100));
     }
@@ -728,7 +728,7 @@ ATTRIBUTE_ISR void UART1_IRQHandler(void)
         fifos = port->regs->UR_FIFOS;
         uart_handle_cts_change(port, fifos & UFS_CST_STS);
     }
-    if (intr_src & UIS_RX_FIFO_TIMEOUT)
+    if (port->rx_callback != NULL && intr_src & UIS_RX_FIFO_TIMEOUT)
     {
         port->rx_callback(0, (void*)((int)port->priv_data+100));
     }
@@ -816,7 +816,7 @@ ATTRIBUTE_ISR void UART2_4_IRQHandler(void)
         fifos = port->regs->UR_FIFOS;
         uart_handle_cts_change(port, fifos & UFS_CST_STS);
     }
-    if (intr_src & UIS_RX_FIFO_TIMEOUT)
+    if (port->rx_callback != NULL && intr_src & UIS_RX_FIFO_TIMEOUT)
     {
         port->rx_callback(0, (void*)((int)port->priv_data+100));
     }