Add validity check for key names when writing

Adds a simple sanity check for key names when users are
writing data to AstDB. This captures four cases indicating
malformed keynames that generally result in bad data going
into the DB that the user didn't intend: an empty key name,
a key name beginning or ending with a slash, and a key name
containing two slashes in a row. Generally, this is the
result of a variable being used in the key name being empty.

If a malformed key name is detected, a warning is emitted
to indicate the bug in the dialplan.

<asterisk/asterisk@b1765c9>

asterisk/funcs/func_db.c

@@ -95,6 +95,14 @@ static int function_db_write(struct ast_channel *chan, char *cmd, char *parse,
 		return -1;
 	}
 
+	/*
+	* When keynames are dynamically created using variables, if the variable is empty, this put bad data into the DB.
+	* In particular, a few cases: an empty key name, a key starting or ending with a /, and a key containing // two slashes.
+	* If this happens, allow it to go in, but warn the user of the issue and possible data corruption. */
+	if (ast_strlen_zero(args.key) || args.key[0] == '/' || args.key[strlen(args.key) - 1] == '/' || strstr(args.key, "//")) {
+		ast_log(LOG_WARNING, "DB: key '%s' seems malformed\n", args.key);
+	}
+
 	if (ast_db_put(args.family, args.key, (char *) value))
 		ast_log(LOG_WARNING, "DB: Error writing value to database.\n");