examples/x11.c: remove dead assigments of some return values

Detected by clang scan in line 212, column 9.
Detected by clang scan in line 222, column 13.
Detected by clang scan in	line 410, column 13.
examples/x11.c: fix result of operation is garbage or undefined

Fix use of uninitialized structure w_size_bck.
Detected by clang scan in	line 386, column 28.
knownhost.c: fix use of uninitialized argument variable wrote

Detected by clang scan in	line 1195, column 18.