always clear fileUploadPreview directive element on preview change
always clear fileUploadPreview directive element on preview change

Verde1705/verde1705.github.io,blueimp/jQuery-File-Upload,blueimp/jQuery-File-Upload,blueimp/jQuery-File-Upload,blueimp/jQuery-File-Upload,Verde1705/verde1705.github.io,blueimp/jQuery-File-Upload,blueimp/jQuery-File-Upload