Check for no key_mgmt/proto/auth_alg entries in config writer

This is not really necessary check, but it keeps a static analyzer
happier by avoiding dead increment. Doing it this way rather than
removing the increment is less likely to cause problems when new entries
are added here in the future (the "dead" increment would be very much
needed in those cases).

Signed-off-by: Jouni Malinen <j@w1.fi>

wpa_supplicant/config.c

@@ -467,6 +467,11 @@ static char * wpa_config_write_proto(const struct parse_data *data,
 		pos += ret;
 	}
 
+	if (pos == buf) {
+		os_free(buf);
+		buf = NULL;
+	}
+
 	return buf;
 }
 #endif /* NO_CONFIG_WRITE */
@@ -672,6 +677,11 @@ static char * wpa_config_write_key_mgmt(const struct parse_data *data,
 	}
 #endif /* CONFIG_WPS */
 
+	if (pos == buf) {
+		os_free(buf);
+		buf = NULL;
+	}
+
 	return buf;
 }
 #endif /* NO_CONFIG_WRITE */
@@ -863,6 +873,11 @@ static char * wpa_config_write_auth_alg(const struct parse_data *data,
 		pos += ret;
 	}
 
+	if (pos == buf) {
+		os_free(buf);
+		buf = NULL;
+	}
+
 	return buf;
 }
 #endif /* NO_CONFIG_WRITE */