[discoverer] Use 'no-more-pads' information
Submitted by Edward Hervey @bilboed
Assigned to Edward Hervey @bilboed
Description
Currently we're not connected to 'no-more-pads' when discovering files and we stop discovering as soon as we have pre-rolled, which is not completely valid (for example the fluendo asf demuxer will create pads as it discovers the muxed buffers, and WILL emit 'no-more-pads' once it has create the pads for all the active streams).
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=353859