Situatuions that terminal window won't be launched

Signed-off-by: Yunlu Zhang <Yunlu.Zhang@synopsys.com>

In this patch terminal won't be launched if user leaves value as an empty
string for COM port, and also won't be launched if user choose "Generic
gdbserver".
Fix the problem of CommandTab when typing command

Signed-off-by: Yunlu Zhang <Yunlu.Zhang@synopsys.com>