avcodec/jpeg2000dwt: assert that mod == 0 for encoding

We are missing the handling of some special cases for this.
These cases should be unused and there should be no reason
to ever use them unless some spec dictates their use
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/jpeg2000dwt.c

@@ -25,6 +25,7 @@
  * Discrete wavelet transform
  */
 
+#include "libavutil/avassert.h"
 #include "libavutil/common.h"
 #include "libavutil/mem.h"
 #include "jpeg2000dwt.h"
@@ -109,6 +110,7 @@ static void dwt_encode53(DWTContext *s, int *t)
             lp;
         int *l;
 
+        av_assert1(!mh && !mv);
         // HOR_SD
         l = line + mh;
         for (lp = 0; lp < lv; lp++){
@@ -179,6 +181,7 @@ static void dwt_encode97_float(DWTContext *s, float *t)
             lp;
         float *l;
 
+        av_assert1(!mh && !mv);
         // HOR_SD
         l = line + mh;
         for (lp = 0; lp < lv; lp++){
@@ -250,6 +253,8 @@ static void dwt_encode97_int(DWTContext *s, int *t)
             lp;
         int *l;
 
+        av_assert1(!mh && !mv);
+
         // HOR_SD
         l = line + mh;
         for (lp = 0; lp < lv; lp++){