FIX does not insert images to activity / invalid sql query id IN ORDER BY 

When uploading an image with an activity, the html code for the image(s) is not written, the ul list is generated but contains no li items.

Debug:
RTMediaModel->get() is invoked with a columns array like array('id' => array(123)) - and this results in an invalid sql string like  "id IN ORDER BY " - the (123) is missing.

if ( ! isset ( $colvalue[ 'value' ] ) ) {
    $colvalue[ 'value' ] = $colvalue;
} 
Is invoked, but $colvalue[ 'value' ] does not contain a value and thus $col_val_comapare is empty.

This fix handles this case.