config: Do not access negative indexes of seen array

Signed-off-by: Jakub Jelen <jjelen@redhat.com>

src/config.c

@@ -383,7 +383,8 @@ static int ssh_config_parse_line(ssh_session session, const char *line,
   }
 
   opcode = ssh_config_get_opcode(keyword);
-  if (*parsing == 1 && opcode != SOC_HOST && opcode != SOC_UNSUPPORTED && opcode != SOC_INCLUDE) {
+  if (*parsing == 1 && opcode != SOC_HOST && opcode != SOC_INCLUDE &&
+      opcode > SOC_UNSUPPORTED) { /* Ignore all unknown types here */
       if (seen[opcode] != 0) {
           SAFE_FREE(x);
           return 0;