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/scripts/didump.lua

@@ -488,7 +488,7 @@ local function readtag(mfkey, aeskey )
 
     for blockNo = 0, numBlocks-1 do
 
-        if core.ukbhit() then
+        if core.kbd_enter_pressed() then
             print("[fail] aborted by user")
             return nil
         end