Fix a mostly harmless warning

In `hexToKeysWithNumpad`, have a default case, a pointless one, because we never
take that branch, but it silences a warning.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/Kaleidoscope/Unicode.cpp

@@ -179,6 +179,9 @@ __attribute__((weak)) Key hexToKeysWithNumpad(uint8_t hex) {
     case 0xF:
       m = Key_F.keyCode;
       break;
+    default:
+      m = Key_NoKey.keyCode;
+      break;
     }
   }
   return { m, KEY_FLAGS };