libsysprof-profile: flush writer when recording stops

We need to at least submit this data to the underlying FD from our buffer
when we stop recording so that anyone consuming the FD will have access to
it. (Such as a SysprofDocumentLoader via FD).

src/libsysprof-profile/sysprof-recording.c

@@ -215,6 +215,9 @@ stop_recording:
   /* Update start/end times to be the "running time" */
   _sysprof_capture_writer_set_time_range (self->writer, begin_time, end_time);
 
+  /* Clear buffers and ensure the disk layer has access to them */
+  sysprof_capture_writer_flush (self->writer);
+
   if (error != NULL)
     return dex_future_new_for_error (g_steal_pointer (&error));