Fix possible missing NUL at end of string

There are were a few uses of 'strncpy' that could lead to a missing NUL,
resulting in possible garbage being displayed. As suggested by Tamas,
use 'wstrlcpy' instead

src/defaults.c

@@ -2005,7 +2005,7 @@ static int getKeybind(WScreen * scr, WDefaultEntry * entry, WMPropList * value,
 		return True;
 	}
 
-	strncpy(buf, val, MAX_SHORTCUT_LENGTH);
+	wstrlcpy(buf, val, MAX_SHORTCUT_LENGTH);
 
 	b = (char *)buf;