sorcery: Use more compatible regex for local expressions.

This changes the use of an empty regex for both res_sorcery_config
and res_sorcery_memory to "." instead. This is a more compatible
regular expression which also works on FreeBSD.

ASTERISK-26206 #close

Change-Id: Ia9166dd176f1597555ba22b6931180d0626c1388

res/res_sorcery_config.c

@@ -210,6 +210,10 @@ static void sorcery_config_retrieve_regex(const struct ast_sorcery *sorcery, voi
 		.regex = &expression,
 	};
 
+	if (ast_strlen_zero(regex)) {
+		regex = ".";
+	}
+
 	if (!config_objects || regcomp(&expression, regex, REG_EXTENDED | REG_NOSUB)) {
 		return;
 	}

res/res_sorcery_memory.c

@@ -188,6 +188,10 @@ static void sorcery_memory_retrieve_regex(const struct ast_sorcery *sorcery, voi
 		.regex = &expression,
 	};
 
+	if (ast_strlen_zero(regex)) {
+		regex = ".";
+	}
+
 	if (regcomp(&expression, regex, REG_EXTENDED | REG_NOSUB)) {
 		return;
 	}