[lib][fuzz] Assert sequences are valid in round trip tests

lib/decompress/zstd_decompress.c

@@ -114,6 +114,9 @@ static void ZSTD_initDCtx_internal(ZSTD_DCtx* dctx)
     dctx->oversizedDuration = 0;
     dctx->bmi2 = ZSTD_cpuid_bmi2(ZSTD_cpuid());
     dctx->outBufferMode = ZSTD_obm_buffered;
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+    dctx->dictContentEndForFuzzing = NULL;
+#endif
 }
 
 ZSTD_DCtx* ZSTD_initStaticDCtx(void *workspace, size_t workspaceSize)
@@ -1039,6 +1042,9 @@ static size_t ZSTD_refDictContent(ZSTD_DCtx* dctx, const void* dict, size_t dict
     dctx->virtualStart = (const char*)dict - ((const char*)(dctx->previousDstEnd) - (const char*)(dctx->prefixStart));
     dctx->prefixStart = dict;
     dctx->previousDstEnd = (const char*)dict + dictSize;
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+    dctx->dictContentEndForFuzzing = dctx->previousDstEnd;
+#endif
     return 0;
 }