minor refactor

added some traces and assert
related to hunting a potential ubsan error in 32-bits more
(it ends up being a compiler-side issue : https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82802).

Modified one pointer arithmetic expression for a more conformant way.

tests/zstreamtest.c

@@ -951,7 +951,7 @@ static int fuzzerTests(U32 seed, U32 nbTests, unsigned startTest, double compres
             for (n=0, cSize=0, totalTestSize=0 ; totalTestSize < maxTestSize ; n++) {
                 /* compress random chunks into randomly sized dst buffers */
                 {   size_t const randomSrcSize = FUZ_randomLength(&lseed, maxSampleLog);
-                    size_t const srcSize = MIN (maxTestSize-totalTestSize, randomSrcSize);
+                    size_t const srcSize = MIN(maxTestSize-totalTestSize, randomSrcSize);
                     size_t const srcStart = FUZ_rand(&lseed) % (srcBufferSize - srcSize);
                     size_t const randomDstSize = FUZ_randomLength(&lseed, maxSampleLog);
                     size_t const dstBuffSize = MIN(cBufferSize - cSize, randomDstSize);
@@ -1564,6 +1564,7 @@ static int fuzzerTests_newAPI(U32 seed, U32 nbTests, unsigned startTest, double
                 size_t const srcStart = FUZ_rand(&lseed) % (srcBufferSize - srcSize);
                 size_t const randomDstSize = FUZ_randomLength(&lseed, maxSampleLog+1);
                 size_t const dstBuffSize = MIN(cBufferSize - cSize, randomDstSize);
+                DISPLAYLEVEL(2, "dstBuffSize : %u \n", (U32)dstBuffSize);
                 ZSTD_EndDirective const flush = (FUZ_rand(&lseed) & 15) ? ZSTD_e_continue : ZSTD_e_flush;
                 ZSTD_inBuffer inBuff = { srcBuffer+srcStart, srcSize, 0 };
                 outBuff.size = outBuff.pos + dstBuffSize;