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More compute_allocation() fixes.

1) Continue to update left and percoeff if we skip all the way to the
    first band.
   This doesn't actually matter for correctness, but I don't want to
    try to explain in a spec why we aren't doing this.
2) Force all the bits in skipped bands to go to fine energy.
   Before some of them could continue to be given to pulses, even though no
    pulses would actually be allocate for them.

--- a/libcelt/rate.c

+++ b/libcelt/rate.c

@@ -203,20 +203,25 @@

       psum += tmp;

    }

-   /*Decide which bands to skip, working backwards from the end.

-     The loop condition stops before the first band, which we never skip: we'd

-      be coding a bit to signal that we're going to waste all the other bits.*/

-   codedBands=end;

-   for (j=end;--j>start;)

+   /* Decide which bands to skip, working backwards from the end. */

+   for (codedBands=end;;codedBands--)

    {

       int band_width;

       int band_bits;

       int rem;

+      j = codedBands-1;

       /*Figure out how many left-over bits we would be adding to this band.

         This can include bits we've stolen back from higher, skipped bands.*/

       left = total-psum;

       percoeff = left/(m->eBands[codedBands]-m->eBands[start]);

       left -= (m->eBands[codedBands]-m->eBands[start])*percoeff;

+      /* Never skip the first band: we'd be coding a bit to signal that we're

+          going to waste all the other bits.

+         This means we won't be using the extra bit we reserved to signal the

+          end of manual skipping, but that will get added back in by

+          quant_all_bands().*/

+      if (j<=start)

+         break;

       rem = IMAX(left-(m->eBands[j]-m->eBands[start]),0);

       band_width = m->eBands[codedBands]-m->eBands[j];

       band_bits = bits[j] + percoeff*band_width + rem;

@@ -257,7 +262,6 @@

          /*Otherwise this band gets nothing at all.*/

          bits[j] = 0;

       }

-      codedBands--;

    }

    /* Allocate the remaining bits */

@@ -272,7 +276,7 @@

       }

    }

    /*for (j=0;j<end;j++)printf("%d ", bits[j]);printf("\n");*/

-   for (j=start;j<end;j++)

+   for (j=start;j<codedBands;j++)

    {

       int N0, N, den;

       int offset;

@@ -324,6 +328,14 @@

       bits[j] -= C*ebits[j]<<BITRES;

       celt_assert(bits[j] >= 0);

       celt_assert(ebits[j] >= 0);

+   }

+   /* The skipped bands use all their bits for fine energy. */

+   for (;j<end;j++)

+   {

+      ebits[j] = bits[j]/C >> BITRES;

+      celt_assert(C*ebits[j]<<BITRES == bits[j]);

+      bits[j] = 0;

+      fine_priority[j] = 0;

    }

    RESTORE_STACK;

    return codedBands;