knownhosts: Avoid possible memory leak on failed malloc

Thanks oss-fuzz

https://issues.oss-fuzz.com/issues/489362256

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Eshan Kelkar <eshankelkar@galorithm.com>

src/knownhosts.c

@@ -310,7 +310,11 @@ static int ssh_known_hosts_read_entries(const char *match,
             }
         }
         if (entry != NULL) {
-            ssh_list_append(*entries, entry);
+            rc = ssh_list_append(*entries, entry);
+            if (rc != SSH_OK) {
+                ssh_knownhosts_entry_free(entry);
+                goto error;
+            }
         }
     }