Problem:
When nvim_input is followed immediately by non-fast events on RPC, both
events and input are available after the polling done by the os_inchar()
in state_enter(), but state_enter() then chooses to process events even
if input is available, which is inconsistent with state_handle_k_event()
that stops processing events once input is available.
Solution:
Also check for available input after the os_inchar() in state_enter().