Fix inflateBack() bug that would fail to detect a too far back.

The bug would pass off an invalid deflate stream as good, and copy
uninitialized memory contents to the output.

infback.c

diff --git a/infback.c b/infback.c
index e6443fe..ac96ba1 100644
--- a/infback.c
+++ b/infback.c
@@ -423,8 +423,6 @@
             /* use inflate_fast() if we have enough input and output */
             if (have >= 6 && left >= 258) {
                 RESTORE();
-                if (state->whave < state->wsize)
-                    state->whave = state->wsize - left;
                 inflate_fast(strm, state->wsize);
                 LOAD();
                 break;