fix another ubsan warning in lz4hc because ubsan complains even about intermediate pointer arithmetic results (in a simple linear formula with 3 factors for example). use parenthesis to make sure calculations go directly from one valid memory address to another valid memory address value.

diff --git a/lib/lz4hc.c b/lib/lz4hc.c
index cf77a0a..33b5de4 100644
--- a/lib/lz4hc.c
+++ b/lib/lz4hc.c

@@ -366,7 +366,7 @@
                 if ( (repeat == rep_confirmed) && (matchCandidateIdx >= lowestMatchIndex)
                   && LZ4HC_protectDictEnd(prefixIdx, matchCandidateIdx) ) {
                     const int extDict = matchCandidateIdx < prefixIdx;
-                    const BYTE* const matchPtr = (extDict ? dictStart - dictIdx : prefixPtr - prefixIdx) + matchCandidateIdx;
+                    const BYTE* const matchPtr = extDict ? dictStart + (matchCandidateIdx - dictIdx) : prefixPtr + (matchCandidateIdx - prefixIdx);
                     if (LZ4_read32(matchPtr) == pattern) {  /* good candidate */
                         const BYTE* const iLimit = extDict ? dictEnd : iHighLimit;
                         size_t forwardPatternLength = LZ4HC_countPattern(matchPtr+sizeof(pattern), iLimit, pattern) + sizeof(pattern);