Wire: allow scanning bus via beginTransmission - endTransmission

[facchinm]

Using

beginTransmission(); 
endTransmission() 

to scan the I2C bus for devices is a very common practice.
The patch solves the case when no byte was sent, only the address to be acknowledged.

Supersedes #39

[ArduinoBot]

✅ Build completed.

⬇️ Build URL: http://downloads.arduino.cc/PR/samd/package_samd-b33_index.json

ℹ️ To test this build:

1. Open the Preferences of the Arduino IDE.
2. Add the Build URL above in the Additional Boards Manager URLs field, and click OK.
3. Open the Boards Manager (menu Tools->Board->Board Manager...)
4. Install Arduino SAMD core - Pull Request Wire: allow scanning bus via beginTransmission - endTransmission #40
5. Select one of the boards under SAMD Pull Request Wire: allow scanning bus via beginTransmission - endTransmission #40 in Tools->Board menu
6. Compile/Upload as usual