fix root cause of #3416

A minor change in 5434de0 changed a `<=` into a `<`,
and as an indirect consequence allowed compression attempt of literals when there are only 6 literals to compress
(previous limit was effectively 7 literals).

This is not in itself a problem, as the threshold is merely an heuristic,
but it emerged a bug that has always been there, and was just never triggered so far due to the previous limit.
This bug would make the literal compressor believes that all literals are the same symbol,
but for the exact case where nbLiterals==6, plus a pretty wild combination of other limit conditions,
this outcome could be false, resulting in data corruption.

Replaced the blind heuristic by an actual test for all limit cases,
so that even if the threshold is changed again in the future,
the detection of RLE mode will remain reliable.

lib/common/huf.h

@@ -221,7 +221,7 @@ size_t HUF_compress4X_repeat(void* dst, size_t dstSize,
                        unsigned maxSymbolValue, unsigned tableLog,
                        void* workSpace, size_t wkspSize,    /**< `workSpace` must be aligned on 4-bytes boundaries, `wkspSize` must be >= HUF_WORKSPACE_SIZE */
                        HUF_CElt* hufTable, HUF_repeat* repeat, int preferRepeat, int bmi2,
-                       unsigned suspectUncompressible, HUF_depth_mode depthMode);
+                       int suspectUncompressible, HUF_depth_mode depthMode);
 
 /** HUF_buildCTable_wksp() :
  *  Same as HUF_buildCTable(), but using externally allocated scratch buffer.
@@ -328,7 +328,7 @@ size_t HUF_compress1X_repeat(void* dst, size_t dstSize,
                        unsigned maxSymbolValue, unsigned tableLog,
                        void* workSpace, size_t wkspSize,   /**< `workSpace` must be aligned on 4-bytes boundaries, `wkspSize` must be >= HUF_WORKSPACE_SIZE */
                        HUF_CElt* hufTable, HUF_repeat* repeat, int preferRepeat, int bmi2,
-                       unsigned suspectUncompressible, HUF_depth_mode depthMode);
+                       int suspectUncompressible, HUF_depth_mode depthMode);
 
 size_t HUF_decompress1X1 (void* dst, size_t dstSize, const void* cSrc, size_t cSrcSize);   /* single-symbol decoder */
 #ifndef HUF_FORCE_DECOMPRESS_X1