MFXVideoENCODE_Query calls CheckVideoParamQueryLike in MSDK and
will determine whether to set param.mfx.TargetKbps to the allowed
minTargetKbps according to the bitrate_limit in extco2 buffer.

Thus q->param.ExtParam must be set before MFXVideoENCODE_Query in case
minTargetKbps is written to TargetKbps by default.

1080P AVC encoding with option "-bitrate_limit 0 -b:v 100k":
Before patch:
            902 kbps
After patch:
            156 kbps
Signed-off-by: Linjie Fu <linjie.fu@intel.com>