Fix cut-and-paste errors in nonfatal() implementations.

Unix GUI programs should not say 'Fatal Error' in the message box
title, and Plink should not destroy its logging context as a side
effect of printing a non-fatal error. Both appear to have been due to
inattentive cut and paste from the pre-existing fatal error functions.

[originally from svn r10044]

windows/winplink.c

@@ -57,10 +57,6 @@ void nonfatal(char *p, ...)
     vfprintf(stderr, p, ap);
     va_end(ap);
     fputc('\n', stderr);
-    if (logctx) {
-        log_free(logctx);
-        logctx = NULL;
-    }
 }
 void connection_fatal(void *frontend, char *p, ...)
 {