fixed #718, reported by @GregSlazinski, solution suggested by @mcmilk

lib/common/zstd_internal.h

@@ -331,4 +331,16 @@ size_t ZSTD_compressStream_generic(ZSTD_CStream* zcs,
 ZSTD_parameters ZSTD_getParamsFromCDict(const ZSTD_CDict* cdict);
 
 
+typedef struct {
+    blockType_e blockType;
+    U32 lastBlock;
+    U32 origSize;
+} blockProperties_t;
+
+/*! ZSTD_getcBlockSize() :
+*   Provides the size of compressed block from block header `src` */
+size_t ZSTD_getcBlockSize(const void* src, size_t srcSize,
+                          blockProperties_t* bpPtr);
+
+
 #endif   /* ZSTD_CCOMMON_H_MODULE */