QSV: fix a compiler warning ('expected declaration').
QSV: work around an issue caused by forcing a keyframe at chapter points.

If:

- chapter markers are enabled
- we insert an IDR right after another IDR (selected by MSDK)
- B-pyramid is enabled

…then sometimes Media SDK will use a B-reference instead of
a P-frame; the problem with that being that the number of
consecutive B-reference then exceeds the maximum allowed by
the initial Decode Time Stamp delay, resulting in PTS < DTS
for the first non-reference B-frame following it.

Note: we can't fall back to the MSDK-provided DTS, as it's
also invalid in that case (less than the previous DTS, so
not monotonically increasing). We also can't set DTS = PTS,
since the PTS was already used as another frame's DTS (this
would result in a non-monotonically increasing DTS too).