libavcodec/tests/motion: Add check for avcodec_alloc_context3()

Add check for the return value of avcodec_alloc_context3() to avoid potential NULL pointer dereference.

Fixes: 5d48e4eafa ("Merge commit 'a6a750c7ef240b72ce01e9653343a0ddf247d196'")
Signed-off-by: Jiasheng Jiang <jiashengjiangcool@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/tests/motion.c

@@ -129,6 +129,10 @@ int main(int argc, char **argv)
     printf("ffmpeg motion test\n");
 
     ctx = avcodec_alloc_context3(NULL);
+    if (!ctx) {
+        return 1;
+    }
+
     ctx->flags |= AV_CODEC_FLAG_BITEXACT;
     av_force_cpu_flags(0);
     ff_me_cmp_init(&cctx, ctx);