Remove unused +1 on doc buffer length. (#14043)

We no longer take advantatge of it.

lucene/core/src/java/org/apache/lucene/codecs/lucene101/Lucene101PostingsReader.java

@@ -297,7 +297,7 @@ final class BlockPostingsEnum extends ImpactsEnum {
     private ForDeltaUtil forDeltaUtil;
     private PForUtil pforUtil;
 
-    private final int[] docBuffer = new int[BLOCK_SIZE + 1];
+    private final int[] docBuffer = new int[BLOCK_SIZE];
 
     private int doc; // doc we last read
 
@@ -418,10 +418,6 @@ public BlockPostingsEnum(FieldInfo fieldInfo, int flags, boolean needsImpacts)
       this.needsImpacts = needsImpacts;
       needsDocsAndFreqsOnly = needsPos == false && needsImpacts == false;
 
-      // We set the last element of docBuffer to NO_MORE_DOCS, it helps save conditionals in
-      // advance()
-      docBuffer[BLOCK_SIZE] = NO_MORE_DOCS;
-
       if (needsFreq == false) {
         Arrays.fill(freqBuffer, 1);
       }
@@ -586,7 +582,6 @@ private void refillFullBlock() throws IOException {
       prevDocID = docBuffer[BLOCK_SIZE - 1];
       docBufferUpto = 0;
       posDocBufferUpto = 0;
-      assert docBuffer[docBufferSize] == NO_MORE_DOCS;
     }
 
     private void refillRemainder() throws IOException {