examples: avoid use of uninitialized variable 'sock'

example/sftp_write.c

@@ -88,7 +88,7 @@ int main(int argc, char *argv[])
     local = fopen(loclfile, "rb");
     if (!local) {
         printf("Can't local file %s\n", loclfile);
-        goto shutdown;
+        return -1;
     }
 
     /*