Fix sending End Of Stream on gst plugin

When streaming to gst a typefind operation
is performed which jumps around to find which
codec the file provides, this fix the call to
send an EOS before we try to read and not after
which causes confusion to gst.

Task-number: QTBUG-32963
Change-Id: I2658b6a4e960430c8ab422a3bee5e11956663116
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>