Fixes #82: Missing sync on first transmit.

[sergiitk]

What's this PR do?

• Fixes an issue with sync (preamble) being sent after first code transmission

Testing

I used 2 Arduinos:

1. 433 Mhz receiver that coded to blink when the right code is caught
2. 433 Mhz transmitter that sends the code. I reverse-engineered it from my garage door RC (HS1527 chip)

Then I set mySwitch.setRepeatTransmit(); on the transmitter (2) to a minimum that the receiver (1) would catch every time, in my case 4 times. When set to 3, receiver (1) couldn't catch it.

After the change receiver (1) started to catch the code every time with mySwitch.setRepeatTransmit(3); set.

What are the relevant tickets?

Fixes #82.

[Martin-Laclaustra]

Please see my comment in #82. This may be due to the way that RCSwitch decodes, but the original remotes might not send the signal as you propose.

[Martin-Laclaustra]

Confirmed, the original chips send the sync bit after data bits.
See: [https://www.digchip.com/datasheets/parts/datasheet/433/SC5262.php]
The SC5262 sends the codes with the sync bit after the address+data bits (12 tri-state bits).

[sui77]

why not both? start with a sync bit and allways end with a sync bit. this way devices detecting sync at start would catch the first repetition and devices detecting sync at end would not miss the last repetition.
(see my change, didn't test that yet)