Fix track-services bad output if server exit

If the server exit while a track-services command is running, then
adb_connect_command returns and the flow goes into the incorrect
"unknown mdns command [%s]".

Test: NA
Bug: NA
Flag: EXEMPT (adb.exe)
Change-Id: If5654d389d3761faf195c52223270877f9d2666f
1 file changed