Error checking in readRegister

[fl4p]

Hi,

readRegister misses error checking of the i2c calls. If for example requestFrom fails, i.e. returns 0, or no data is available, the function returns 0. This causesgetBusVoltage_V to return zero when there is a problem with the i2c bus, so we don't know if the read failed or actually reading zero voltage.

[wollewald]

@fl4p, I added the function getI2cErrorCode() which return the return value of endTransmission. I updated the example sketches Trigger.ino and Continuous.ino to show how it works.

I have also added a timeout check for startSingleMeasurement() of 2 seconds to avoid that the program hangs forever in case of unavailability of the INA226.

The changes are implemented in the new release 1.2.7.