avutil/fixed_dsp: Check for av_malloc() failure

Fixes CID1271051
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/fixed_dsp.c

@@ -91,6 +91,10 @@ static void vector_fmul_window_fixed_c(int32_t *dst, const int32_t *src0,
 AVFixedDSPContext * avpriv_alloc_fixed_dsp(int bit_exact)
 {
     AVFixedDSPContext * fdsp = av_malloc(sizeof(AVFixedDSPContext));
+
+    if (!fdsp)
+        return NULL;
+
     fdsp->vector_fmul_window_scaled = vector_fmul_window_fixed_scaled_c;
     fdsp->vector_fmul_window = vector_fmul_window_fixed_c;