input: add an option to force preparsing

For input items without a know type (imem access for example) preparsing
is not possible. With this option we allow forcing the preparsing in that
case, optionally. By default the current behavior remains the same.

include/vlc_input_item.h

@@ -483,6 +483,7 @@ typedef enum input_item_meta_request_option_t
     META_REQUEST_OPTION_FETCH_NETWORK = 0x08,
     META_REQUEST_OPTION_FETCH_ANY     = 0x0C,
     META_REQUEST_OPTION_DO_INTERACT   = 0x10,
+    META_REQUEST_OPTION_NO_SKIP       = 0x20,
 } input_item_meta_request_option_t;
 
 /* status of the on_preparse_ended() callback */

src/preparser/preparser.c

@@ -323,6 +323,7 @@ int input_preparser_Push( input_preparser_t *preparser,
         item->b_preparse_interact = true;
     vlc_mutex_unlock( &item->lock );
 
+    if (!(i_options & META_REQUEST_OPTION_NO_SKIP))
     switch( i_type )
     {
         case ITEM_TYPE_NODE: