Don't memzero() the history buffer when initializing LZ

decoder. There's no danger of information leak here, so
it isn't required. Doing memzero() takes a lot of time
with large dictionaries, which could make it easier to
construct DoS attack to consume too much CPU time.

src/liblzma/lz/lz_decoder.c

@@ -429,10 +429,9 @@ lzma_lz_decoder_reset(lzma_lz_decoder *lz, lzma_allocator *allocator,
 			return LZMA_MEM_ERROR;
 	}
 
-	// Clean up the buffers to make it very sure that there are
+	// Clean up the temporary buffer to make it very sure that there are
-	// no information leaks when multiple steams are decoded
+	// no information leaks when multiple steams are decoded with the
-	// with the same decoder structures.
+	// same decoder structures.
-	memzero(lz->dict, dict_real_size);
 	memzero(lz->temp, LZMA_BUFFER_SIZE);
 
 	// Reset the variables so that lz_get_byte(lz, 0) will return '\0'.