[minor] Improve docs and add an assert in response to review

lib/compress/zstd_compress.c

@@ -1069,6 +1069,7 @@ U32 ZSTD_cycleLog(U32 hashLog, ZSTD_strategy strat)
  * is within the window. So the hashLog and chainLog should be large enough to reference both
  * the dictionary and the window. So we must use this adjusted dictAndWindowLog when downsizing
  * the hashLog and windowLog.
+ * NOTE: srcSize must not be ZSTD_CONTENTSIZE_UNKNOWN.
  */
 static U32 ZSTD_dictAndWindowLog(U32 windowLog, U64 srcSize, U64 dictSize)
 {
@@ -1077,6 +1078,7 @@ static U32 ZSTD_dictAndWindowLog(U32 windowLog, U64 srcSize, U64 dictSize)
     if (dictSize == 0) {
         return windowLog;
     }
+    assert(windowLog <= ZSTD_WINDOWLOG_MAX);
     assert(srcSize != ZSTD_CONTENTSIZE_UNKNOWN); /* Handled in ZSTD_adjustCParams_internal() */
     {
         U64 const windowSize = 1ULL << windowLog;