tools/target_dec_fuzzer: consider potential padding/edge in pixel threshold

Fixes: Timeout (73sec ->30ms)
Fixes: 16921/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_DIRAC_fuzzer-5689384594046976

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

tools/target_dec_fuzzer.c

@@ -259,7 +259,7 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
             av_frame_unref(frame);
             int ret = decode_handler(ctx, frame, &got_frame, &avpkt);
 
-            ec_pixels += ctx->width * ctx->height;
+            ec_pixels += (ctx->width + 32LL) * (ctx->height + 32LL);
             if (it > 20 || ec_pixels > 4 * ctx->max_pixels)
                 ctx->error_concealment = 0;
             if (ec_pixels > maxpixels)