capture-cursor: reset reader upon creation

When creating our private reader copy, we need to reset the
reader so that we start at the beginning. Otherwise, we are
likely to be at the end of the capture (especially for in
memory captures).

lib/sp-capture-cursor.c

@@ -199,6 +199,7 @@ sp_capture_cursor_new (SpCaptureReader *reader)
 
   self = g_object_new (SP_TYPE_CAPTURE_CURSOR, NULL);
   self->reader = sp_capture_reader_copy (reader);
+  sp_capture_reader_reset (self->reader);
 
   return self;
 }