vorbis_psy: fix the half-octave bounds check in _vp_psy_init

Reported-by: Dutchman101 "<[email protected]>"

Original commit message from the equivalent vorbis patch:

> The existing code ensured that halfoc would not exceed P_BANDS-1,
>  but the interpolation used index P_BANDS (albeit with a weight
>  of 0) when this bound was actually hit.
> Add an extra clamp on the integer index to avoid this.
> Thanks to Paul Adenot for the report.

See the original vorbis patch here:
https://gitlab.xiph.org/xiph/vorbis/-/commit/315da9cc9d30484c802b2e2ea150df39e060e2b9.patch

Signed-off-by: Tristan Matthews <[email protected]>

Author: Timothy B. Terriberry

libspeex/vorbis_psy.c

@@ -340,6 +340,10 @@ VorbisPsy *vorbis_psy_init(int rate, int n)
     if(halfoc<0)halfoc=0;
     if(halfoc>=P_BANDS-1)halfoc=P_BANDS-1;
     inthalfoc=(int)halfoc;
+    /*If we hit the P_BANDS-1 clamp above, inthalfoc+1 will be out of bounds,
+       even though it will have an interpolation weight of 0.
+      Shift the interval so we don't read past the end of the array.*/
+    if(inthalfoc>=P_BANDS-2)inthalfoc=P_BANDS-2;
     del=halfoc-inthalfoc;
 
     p->noiseoffset[i]=