SPI.end() does not check for NULL => crashes NANO33

[RobTillaart]

First mentioned here RobTillaart/MS5611_SPI#6

Summary

It should be safe to call SPI.end() before SPI.begin() to allow dynamic change SPI settings.
Now it crashes on the NANO33

Solution

Current code

From - https://github.com/arduino/ArduinoCore-mbed/blob/master/libraries/SPI/SPI.cpp

void arduino::MbedSPI::begin() {
    if (dev == NULL) {
      dev = new mbed_spi;
      dev->obj = NULL;
    }
    if (dev->obj == NULL) {
      dev->obj = new mbed::SPI(_mosi, _miso, _sck);
    }
}

void arduino::MbedSPI::end() {
    if (dev->obj != NULL) {                      //   <<<<<<<<<<  if dev == NULL this crashes.
        delete dev->obj;
    }
}

Proposal

void arduino::MbedSPI::end() {
    if (dev != NULL) {
        if (dev->obj != NULL) {
            delete dev->obj;
        }
    }
}

[arotman]

This is an important bug fix, as the Arduino code dereferences a NULL pointer and just silently crashes. Ugly stuff. But easy to fix.