fix no pointer init value

[PanzerFowst]

So, silly me: I have been banging my head against a wall trying to figure out why I couldn't create an array of Adafruit_PCF8574 classes. Finally broke out the debugger and realized that for some reason, my Arduino board would create blank classes when initializing the array of Adafruit_PCF8574 objects as such:

static Adafruit_PCF8574 pcfList[3];

But then if I tried to create a list like so, it would fail into the dummy_handler() from the delete (i2c_dev); from the begin() function.

static Adafruit_PCF8574* pcfList;

// ...

pcfList = new Adafruit_PCF8574[pcfAddrLen];

Adafruit_PCF8574 pcf;
for (pcfListLen = 0; pcfListLen < pcfAddrLen; pcfListLen++) {

    // Create new Adafruit_PCF8574 object:
    pcf = Adafruit_PCF8574();

    // Attempt to begin communication:
    if (!pcf.begin(pcfAddr[pcfListLen])) {
        SerialUSB.print("Couldn't find PCF8574 at address 0x");
        SerialUSB.println(pcfAddr[pcfListLen]);
        while (1) {}
    }

    // Finally, save object to array list:
    pcfList[pcfListLen] = pcf;
}

Hopefully this is an easy enough fix to merge in.

• Describe the scope of your change--i.e. what the change does and what parts of the code were modified. This will help us understand any risks of integrating the code.

Just initialized the pointers in the class to be nullptr so that it doesn't pick up garbage from memory.

• Describe any known limitations with your change. For example if the change doesn't apply to a supported platform of the library please mention it.

This does not have limitations (unless nullptr is not defined).

• Please run any tests or examples that can exercise your modified code. We strive to not break users of the code and running tests/examples helps with this process.

Passed.