Retrieves a pad from the element by name (e.g. "src_\%d").
This version only retrieves request pads. The pad should be released with release_request_pad.
This method is slower than manually getting the pad template and calling
request_pad if the pads should have a specific name (e.g.
name is "src_1" instead of "src_\%u").
a Element to find a request pad of.
the name of the request Pad to retrieve.
requested Pad if found, otherwise