Fix ArrayCache usage with LZMAInputStream

Add a missing initialization to LZDecoder's constructor. The same
initialization is done in LZDecoder.reset(). LZMA2InputStream
always calls it before decoding anything, thus this bug didn't break
LZMA2 decoding. However, LZMAInputStream has no reason to call
LZDecoder.reset(), and thus the missing initialization in the
constructor meant that ArrayCache didn't work with LZMAInputStream.

Fixes: c5569e4 ("Add ArrayCache support to LZMA and LZMA2 coders, part 1.")
Fixes: #23

Author: Larhzu

src/org/tukaani/xz/lz/LZDecoder.java

@@ -24,6 +24,15 @@ public LZDecoder(int dictSize, byte[] presetDict, ArrayCache arrayCache) {
         bufSize = dictSize;
         buf = arrayCache.getByteArray(bufSize, false);
 
+        // getByte(0) needs to return 0x00 when no data has been decompressed.
+        // This requires initializing only one byte, so don't pass "true" as
+        // the second argument in the above arrayCache.getByteArray call.
+        //
+        // Note that LZMA2InputStream calls LZDecoder.reset() before decoding
+        // anything, thus it doesn't break even if this initialization was
+        // missing here. But LZMAInputStream has no reason to call reset().
+        buf[bufSize - 1] = 0x00;
+
         if (presetDict != null) {
             pos = Math.min(presetDict.length, dictSize);
             full = pos;