res_config_odbc: set empty extended field as a single whitespace

If Realtime @ variable value is NULL or empty or contains only whitespaces
then when we try to retrieve it using PJSIP_ENDPOINT we get WARNING
pjsip_endpoint_function_read: Unknown property @my_var for PJSIP endpoint.
And the variable is missing in the result of CLI pjsip show endpoint.

This patch keeps empty sorcery extended field.

ASTERISK-28341 #close

Change-Id: I221fccc04cbfa2be17ce971f64ae0e74e465eea0

res/res_config_odbc.c

@@ -287,6 +287,20 @@ static struct ast_variable *realtime_odbc(const char *database, const char *tabl
 		}
 
 		stringp = ast_str_buffer(rowdata);
+		if (!strncmp(coltitle, "@", 1)) {
+			/* The '@' prefix indicates it's a sorcery extended field.
+			 * Because ast_load_realtime_fields eliminates empty entries and makes blank (single whitespace)
+			 * entries empty and keeps them, the empty or NULL values are encoded
+			 * as a string containing a single whitespace. */
+			if (prev) {
+				prev->next = ast_variable_new(coltitle, S_OR(stringp," "), "");
+				if (prev->next) {
+					prev = prev->next;
+				}
+			} else {
+				prev = var = ast_variable_new(coltitle, S_OR(stringp," "), "");
+			}
+		} else {
 			while (stringp) {
 				chunk = strsep(&stringp, ";");
 				if (!ast_strlen_zero(ast_strip(chunk))) {
@@ -304,6 +318,7 @@ static struct ast_variable *realtime_odbc(const char *database, const char *tabl
 				}
 			}
 		}
+	}
 
 	SQLFreeHandle(SQL_HANDLE_STMT, stmt);
 	ast_odbc_release_obj(obj);
@@ -451,6 +466,14 @@ static struct ast_config *realtime_multi_odbc(const char *database, const char *
 				goto next_sql_fetch;
 			}
 			stringp = ast_str_buffer(rowdata);
+			if (!strncmp(coltitle, "@", 1)) {
+				/* The '@' prefix indicates it's a sorcery extended field.
+				 * Because ast_load_realtime_fields eliminates empty entries and makes blank (single whitespace)
+				 * entries empty and keeps them, the empty or NULL values are encoded
+				 * as a string containing a single whitespace. */
+				var = ast_variable_new(coltitle, S_OR(stringp," "), "");
+				ast_variable_append(cat, var);
+			} else {
 				while (stringp) {
 					chunk = strsep(&stringp, ";");
 					if (!ast_strlen_zero(ast_strip(chunk))) {
@@ -465,6 +488,7 @@ static struct ast_config *realtime_multi_odbc(const char *database, const char *
 					}
 				}
 			}
+		}
 		ast_category_append(cfg, cat);
 next_sql_fetch:;
 	}