Bug in nrf_serial_read

[Jchristf]

We have found what appears an easily reproducible bug in nrf_serial_read.

Reproduce as follows:

* PCA10040

* SDK 15.3

* SES

* Example project peripheral serial

* Change to Flow control disabled

* Change the timeout parameter on nrf_serial_read to 0 (is 1000)

Now when you do the echo loop occasionally you will see random characters.

I cant see any reason that a zero timeout shouldnt work..?

[Jchristf]

PS: You can close the previous ticket: "Stuck TX interrupt with nrf_serial_write" - it was a bug in receiving terminal.