test for fail to decompress

examples/dictionary_decompression.c

@@ -78,10 +78,14 @@ static void decompress(const char* fname, const ZSTD_DDict* ddict)
     size_t cSize;
     void* const cBuff = loadFile_orDie(fname, &cSize);
     unsigned long long const rSize = ZSTD_findDecompressedSize(cBuff, cSize);
-    if (rSize==ZSTD_CONTENTSIZE_UNKNOWN) {
+    if (rSize==ZSTD_CONTENTSIZE_ERROR) {
+        fprintf(stderr, "%s : it was not compressed by zstd.\n", fname);
+        exit(5);
+    } else if (rSize==ZSTD_CONTENTSIZE_UNKNOWN) {
         fprintf(stderr, "%s : original size unknown \n", fname);
         exit(6);
     }
+
     void* const rBuff = malloc_orDie((size_t)rSize);
 
     ZSTD_DCtx* const dctx = ZSTD_createDCtx();