fix(uart): prevent deinitializing another UART

If called from an uninitialized HardwareSerial, the code unintentionally deinit the UART at uart_handlers[0]

Author: thiagogba

libraries/SrcWrapper/src/stm32/uart.c

@@ -594,6 +594,9 @@ bool uart_init(serial_t *obj, uint32_t baudrate, uint32_t databits, uint32_t par
   */
 void uart_deinit(serial_t *obj)
 {
+  /* Prevent deinitializing another UART in case this has not been initialized */
+  if (!obj->uart) return;
+  
   /* Reset UART and disable clock */
   switch (obj->index) {
 #if defined(USART1_BASE)