avocdec/cavsdsp: Fix undefined pointer arithmetic

src2 is used in CAVS_SUBPIX_HV iff FULL is true (it is exactly
for the egpr functions); otherwise it might be NULL. So check
for FULL before doing pointer arithmetic.
Fixes a "src/libavcodec/cavsdsp.c:524:1: runtime error: applying
non-zero offset 8 to null pointer" from UBSan.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/cavsdsp.c

@@ -425,13 +425,14 @@ static void OPNAME ## cavs_filt8_hv_ ## NAME(uint8_t *dst, const uint8_t *src1,
 \
 static void OPNAME ## cavs_filt16_hv_ ## NAME(uint8_t *dst, const uint8_t *src1, const uint8_t *src2, ptrdiff_t dstStride, ptrdiff_t srcStride)\
 {                                                                       \
-    OPNAME ## cavs_filt8_hv_ ## NAME(dst  , src1,   src2  , dstStride, srcStride); \
-    OPNAME ## cavs_filt8_hv_ ## NAME(dst+8, src1+8, src2+8, dstStride, srcStride); \
+    OPNAME ## cavs_filt8_hv_ ## NAME(dst  , src1,   FULL ? src2     : NULL, dstStride, srcStride); \
+    OPNAME ## cavs_filt8_hv_ ## NAME(dst+8, src1+8, FULL ? src2 + 8 : NULL, dstStride, srcStride); \
     src1 += 8*srcStride;\
-    src2 += 8*srcStride;\
+    if (FULL) \
+        src2 += 8*srcStride;\
     dst += 8*dstStride;\
-    OPNAME ## cavs_filt8_hv_ ## NAME(dst  , src1,   src2  , dstStride, srcStride); \
-    OPNAME ## cavs_filt8_hv_ ## NAME(dst+8, src1+8, src2+8, dstStride, srcStride); \
+    OPNAME ## cavs_filt8_hv_ ## NAME(dst  , src1,   FULL ? src2     : NULL, dstStride, srcStride); \
+    OPNAME ## cavs_filt8_hv_ ## NAME(dst+8, src1+8, FULL ? src2 + 8 : NULL, dstStride, srcStride); \
 }\
 
 #define CAVS_MC(OPNAME, SIZE) \
@@ -492,22 +493,22 @@ static void OPNAME ## cavs_qpel ## SIZE ## _mc33_c(uint8_t *dst, const uint8_t *
 \
 static void OPNAME ## cavs_qpel ## SIZE ## _mc21_c(uint8_t *dst, const uint8_t *src, ptrdiff_t stride)\
 {\
-  OPNAME ## cavs_filt ## SIZE ## _hv_ff(dst, src, src+stride+1,stride, stride); \
+  OPNAME ## cavs_filt ## SIZE ## _hv_ff(dst, src, NULL, stride, stride); \
 }\
 \
 static void OPNAME ## cavs_qpel ## SIZE ## _mc12_c(uint8_t *dst, const uint8_t *src, ptrdiff_t stride)\
 {\
-  OPNAME ## cavs_filt ## SIZE ## _hv_ii(dst, src, src+stride+1,stride, stride); \
+  OPNAME ## cavs_filt ## SIZE ## _hv_ii(dst, src, NULL, stride, stride); \
 }\
 \
 static void OPNAME ## cavs_qpel ## SIZE ## _mc32_c(uint8_t *dst, const uint8_t *src, ptrdiff_t stride)\
 {\
-  OPNAME ## cavs_filt ## SIZE ## _hv_kk(dst, src, src+stride+1,stride, stride); \
+  OPNAME ## cavs_filt ## SIZE ## _hv_kk(dst, src, NULL, stride, stride); \
 }\
 \
 static void OPNAME ## cavs_qpel ## SIZE ## _mc23_c(uint8_t *dst, const uint8_t *src, ptrdiff_t stride)\
 {\
-  OPNAME ## cavs_filt ## SIZE ## _hv_qq(dst, src, src+stride+1,stride, stride); \
+  OPNAME ## cavs_filt ## SIZE ## _hv_qq(dst, src, NULL, stride, stride); \
 }\
 
 #define op_put1(a, b)  a = cm[((b)+4)>>3]