fix extended case combining stableInBuffer with continue() and flush() modes

lib/compress/zstd_compress_internal.h

@@ -410,8 +410,8 @@ struct ZSTD_CCtx_s {
 
     /* Stable in/out buffer verification */
     ZSTD_inBuffer expectedInBuffer;
+    size_t stableIn_notConsumed; /* nb bytes within stable input buffer that are said to be consumed but are not */
     size_t expectedOutBufferSize;
-    size_t savedInPosPlusOne;  /* 0 == no savedInPos */
 
     /* Dictionary */
     ZSTD_localDict localDict;