.png extension not stored to database - php

Question

I am trying to upload images using php and html form.
<form class="form-horizontal" method="POST" action="products_photo.php" enctype="multipart/form-data">
<input type="hidden" class="prodid" name="id">
<div class="form-group">
<label for="photo" class="col-sm-3 control-label">Photo</label>
<div class="col-sm-9">
<input type="file" id="photo" name="photo" required>
</div>
</div>
</div>
<div class="modal-footer">
<button type="button" class="btn btn-default btn-flat pull-left" data-dismiss="modal"><i class="fa fa-close"></i> Close</button>
<button type="submit" class="btn btn-success btn-flat" name="upload"><i class="fa fa-check-square-o"></i> Update</button>
</form>
But the issue is png extensions are not being saved to database. jpg and jpeg are stored.
Anyone has an idea how to solve this?
I am using a function to make slug for images, but the extensions for jpg and jpeg are stored in database but not for png files.
the php file:
<?php
if(isset($_POST['upload'])){
$id = $_POST['id'];
$filename = $_FILES['photo']['name'];
$conn = $pdo->open();
$stmt = $conn->prepare("SELECT * FROM products WHERE id=:id");
$stmt->execute(['id'=>$id]);
$row = $stmt->fetch();
if(!empty($filename)){
$ext = pathinfo($filename, PATHINFO_EXTENSION);
$new_filename = $row['slug'].'_'.time().'.'.$ext;
move_uploaded_file($_FILES['photo']['tmp_name'], '../images/'.$new_filename);
}
try{
$stmt = $conn->prepare("UPDATE products SET photo=:photo WHERE id=:id");
$stmt->execute(['photo'=>$new_filename, 'id'=>$id]);
$_SESSION['success'] = 'Product photo updated successfully';
}
catch(PDOException $e){
$_SESSION['error'] = $e->getMessage();
}
$pdo->close();
}
else{
$_SESSION['error'] = 'Select product to update photo first';
}
?>