Description:
------------
PHP's SQLite3Result::columnName() method produces a segmentation fault when column_number exceeds the column count.

Inside ext/sqlite3/sqlite3.c, PHP utlizes RETVAL_STRING for the data coming back from SQLite's sqlite3_column_name() function.  But inside ext/sqlite3/libsqlite/sqlite3.c, their sqlite3_column_name() function calls columnName(), which returns 0 on error conditions.

PHP's C code needs to be adjusted to account for mixed type results from sqlite3_column_name().  When making this fix, it seems PHP should return FALSE if sqlite3_column_name() produces 0.


Test script:
---------------
$db = new SQLite3(':memory:');

$db->exec('CREATE TABLE test (whatever INTEGER)');
$db->exec('INSERT INTO test (whatever) VALUES (1)');

$result = $db->query('SELECT * FROM test');
while ($row = $result->fetchArray(SQLITE3_NUM)) {
    var_dump($result->columnName(0));  // string(8) "whatever"

    // Seems returning false will be most appropriate.
    var_dump($result->columnName(3));  // Segmentation fault
}

$result->finalize();
$db->close();

echo "Done\n";


Expected result:
----------------
string(8) "whatever"
bool(false)
Done


Actual result:
--------------
string(8) "whatever"
Segmentation fault