[TIMOB-20577] Fix getField context for Windows

[garymathews]

• Bind the ResultSet context to the field call to prevent an invalid pointer

TEST CASE

var booksDB = Ti.Database.open('booksDB');
booksDB.execute('CREATE TABLE IF NOT EXISTS books(id INTEGER PRIMARY KEY AUTOINCREMENT, title TEXT, author TEXT)');
booksDB.execute('REPLACE INTO books (title,author) VALUES (?,?)', ('Great Expectations', 'Charles Dickens'));
var result = booksDB.execute('SELECT * FROM books'),
    getField = result.field; // INVALID
    // getField = result.field.bind(result); // VALID
Ti.API.info('=== RESULT ===');
Ti.API.info('fieldCount: ' + result.fieldCount);
for (var i = 0, j = result.fieldCount; i < j; i++) {
    Ti.API.info(getField(i));
}
Ti.API.info('==============');
result.close();
booksDB.close();

JIRA Ticket