ensure cdict is properly reset to NULL

.github/workflows/dev-long-tests.yml

@@ -67,11 +67,11 @@ jobs:
     - name: thread sanitizer zstreamtest
       run: CC=clang ZSTREAM_TESTTIME=-T3mn make tsan-test-zstream
 
-  ubsan-zstreamtest:
+  uasan-zstreamtest:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # tag=v4.1.1
-    - name: undefined behavior sanitizer zstreamtest
+    - name: ub + address sanitizer on zstreamtest
       run: CC=clang make uasan-test-zstream
 
   # lasts ~15mn

lib/compress/zstdmt_compress.c

@@ -1323,6 +1323,7 @@ size_t ZSTDMT_initCStream_internal(
     /* update dictionary */
     ZSTD_freeCDict(mtctx->cdictLocal);
     mtctx->cdictLocal = NULL;
+    mtctx->cdict = NULL;
     if (dict) {
         if (dictContentType == ZSTD_dct_rawContent) {
             mtctx->inBuff.prefix.start = (const BYTE*)dict;