src/update_handler: use g_seekable_tell() to get size of written data
src/update_handler: use g_seekable_tell() to get size of written data

Documentation of g_output_stream_splice() says:

| Note that if the number of bytes spliced is greater than G_MAXSSIZE,
| then that will be returned, and there is no way to determine the actual
| number of bytes spliced.

As copy_raw_image() performs a sanity check if returned size matches
expected write size, it will not be possible to install an image whose
size exceeds G_MAXSSIZE.

Thus instead of letting g_output_stream_splice() close the output stream, we
leave it open to use g_seekable_tell() on it and obtain the actual size
read (written), even if it exceeds gssize.

Fixes #463.

Signed-off-by: Enrico Joerns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

jluebbe/rauc,ejoerns/rauc,ejoerns/rauc,jluebbe/rauc,jluebbe/rauc,rauc/rauc,rauc/rauc,ejoerns/rauc,rauc/rauc