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Don't allow empty eBands.

Currently compute_ebands()'s attempts to round bands to even sizes
 and enforce size constraints on consecutive bands can leave some
 bands entirely empty (e.g., Fs=8000, frame_size=64, i=11).
This adds a simple post-processing loop to remove such bands.

--- a/libcelt/modes.c

+++ b/libcelt/modes.c

@@ -133,7 +133,7 @@

 static celt_int16 *compute_ebands(celt_int32 Fs, int frame_size, int res, int *nbEBands)

 {

    celt_int16 *eBands;

-   int i, lin, low, high, nBark, offset=0;

+   int i, j, lin, low, high, nBark, offset=0;

    /* All modes that have 2.5 ms short blocks use the same definition */

    if (Fs == 400*(celt_int32)frame_size)

@@ -190,6 +190,12 @@

          eBands[i] -= (2*eBands[i]-eBands[i-1]-eBands[i+1])/2;

       }

    }

+   /* Remove any empty bands. */

+   for (i=j=0;i<*nbEBands;i++)

+      if(eBands[i+1]>eBands[j])

+         eBands[++j]=eBands[i+1];

+   *nbEBands=j;

+

    /*for (i=0;i<=*nbEBands+1;i++)

       printf ("%d ", eBands[i]);

    printf ("\n");