Bug with "image" field

There is a really easy fix for this.

The only reason this problem exists is because the plugin calls the "wp_get_attachment_image" function on whatever is returned, since it expects an attachment ID.

So if a simple check is done on the returned value first, we can change the output based on if it's attachment ID or a file URL.

Inside the image.php file if I add a new variable like this:

$attachment_image = (is_numeric($file)) ? wp_get_attachment_image( $file, $field['image_size'] ) : '<img width="150" height="150" src="'.$file.'" alt="" />';

I can then replace the call to wp_get_attachment_image with the $attachment_image variable instead. If an attachment ID is returned, it works as it always did. But if a file URL is returned (because a custom upload folder was used) the preview image still shows up as expected.

This small change seems to make the plugin work as expected, and removes one of the limitations people may run into.

So the original code looks like this:

		return sprintf(
			'<li class="rwmb-image-item">
				<div class="rwmb-file-icon">%s</div>
				<div class="rwmb-image-overlay"></div>
				<div class="rwmb-image-actions">
					%s
					<a href="#" class="rwmb-image-delete rwmb-file-delete" data-attachment_id="%s"><span class="dashicons dashicons-no-alt"></span></a>
				</div>
				<input type="hidden" name="%s[%s]" value="%s">
			</li>',
			wp_get_attachment_image( $file, $field['image_size'] ),
			$edit_link,
			esc_attr( $file ),
			esc_attr( $attributes['name'] ),
			esc_attr( $index ),
			esc_attr( $file )
		);

And with my changes, it looks like this:

$attachment_image = (is_numeric($file)) ? wp_get_attachment_image( $file, $field['image_size'] ) : '<img width="150" height="150" src="'.$file.'" class="attachment-thumbnail size-thumbnail" alt="" />';
		return sprintf(
			'<li class="rwmb-image-item">
				<div class="rwmb-file-icon">%s</div>
				<div class="rwmb-image-overlay"></div>
				<div class="rwmb-image-actions">
					%s
					<a href="#" class="rwmb-image-delete rwmb-file-delete" data-attachment_id="%s"><span class="dashicons dashicons-no-alt"></span></a>
				</div>
				<input type="hidden" name="%s[%s]" value="%s">
			</li>',
			$attachment_image,
			$edit_link,
			esc_attr( $file ),
			esc_attr( $attributes['name'] ),
			esc_attr( $index ),
			esc_attr( $file )
		);