Replace ukbhit by kbd_enter_pressed, not requiring tcgetattr:

Note that it behaves differently now
* it looks for Enter key only, not any key
* it "eats" the input, no need for (void)getchar() after it
* it works the same no matter the value of ICANON
* the mingw version has been adapted to act the similarly

This should fix its usage on Android where tcgetattr always returns -1

client/lualibs/read15.lua

@@ -133,8 +133,8 @@ end
 -- @return if successfull: an table containing card info
 -- @return if unsuccessfull : nil, error
 local function waitFor15693()
-    print('Waiting for card... press any key to quit')
-    while not core.ukbhit() do
+    print('Waiting for card... press Enter to quit')
+    while not core.kbd_enter_pressed() do
         res, err = read15693()
         if res then return res end
         -- err means that there was no response from card