Backport level 9 single value fix

Change-Id: I141da3cb0337e1e255ed621b1a14667464821459

Author: klauspost

src/compress/flate/deflate.go

@@ -395,7 +395,9 @@ func (d *compressor) deflateLazy() {
 			d.h = newHuffmanEncoder(maxFlateBlockTokens)
 		}
 		var tmp [256]uint16
-		for _, v := range d.window[s.index:d.windowEnd] {
+		toIndex := d.window[s.index:d.windowEnd]
+		toIndex = toIndex[:min(len(toIndex), maxFlateBlockTokens)]
+		for _, v := range toIndex {
 			tmp[v]++
 		}
 		d.h.generate(tmp[:], 15)

src/compress/flate/huffman_bit_writer.go

@@ -620,6 +620,9 @@ func (w *huffmanBitWriter) writeBlockDynamic(tokens *tokens, eof bool, input []b
 	sync = sync || eof
 	if sync {
 		tokens.AddEOB()
+	} else {
+		// Ensure we can always write EOB.
+		tokens.extraHist[0] = 1
 	}
 
 	// We cannot reuse pure huffman table, and must mark as EOF.