app_voicemail: Fix incorrect msg leaving/retrieving an ODBC voicemail

Correct the log warning message shown when ODBC voicemail
retrieve_file is called and there is a null value in the category
column.
A more meaningfull message is now written at debug level.

ASTERISK-27853

Change-Id: Ic36e97d5eb070a23a12ba45972f6b53e2182a3f4

apps/app_voicemail.c

@@ -3978,6 +3978,10 @@ static int retrieve_file(char *dir, int msgnum)
 				generate_msg_id(msg_id);
 				snprintf(rowdata, sizeof(rowdata), "%s", msg_id);
 				odbc_update_msg_id(dir, msgnum, msg_id);
+			} else if (res == SQL_NULL_DATA && !strcasecmp(coltitle, "category")) {
+				/* Ignore null column value for category */
+				ast_debug(3, "Ignoring null category column in ODBC voicemail retrieve_file.\n");
+				continue;
 			} else if (!SQL_SUCCEEDED(res)) {
 				ast_log(AST_LOG_WARNING, "SQL Get Data error! coltitle=%s\n[%s]\n\n", coltitle, sql);
 				goto bail_with_handle;