zstream: treat `Z_BUF_ERROR` as non-fatal

zlib will return `Z_BUF_ERROR` whenever there is more input to inflate
or deflate than there is output to store the result.  This is normal for
us as we iterate through the input, particularly with very large input
buffers.

src/zstream.c

@@ -14,17 +14,22 @@
 #define ZSTREAM_BUFFER_SIZE (1024 * 1024)
 #define ZSTREAM_BUFFER_MIN_EXTRA 8
 
-static int zstream_seterr(git_zstream *zs)
+GIT_INLINE(int) zstream_seterr(git_zstream *zs)
 {
-	if (zs->zerr == Z_OK || zs->zerr == Z_STREAM_END)
+	switch (zs->zerr) {
+	case Z_OK:
+	case Z_STREAM_END:
+	case Z_BUF_ERROR: /* not fatal; we retry with a larger buffer */
 		return 0;
-
-	if (zs->zerr == Z_MEM_ERROR)
+	case Z_MEM_ERROR:
 		giterr_set_oom();
-	else if (zs->z.msg)
+		break;
+	default:
+		if (zs->z.msg)
 			giterr_set_str(GITERR_ZLIB, zs->z.msg);
 		else
 			giterr_set(GITERR_ZLIB, "unknown compression error");
+	}
 
 	return -1;
 }
@@ -119,8 +124,8 @@ int git_zstream_get_output(void *out, size_t *out_len, git_zstream *zstream)
 		else
 			zstream->zerr = deflate(&zstream->z, zflush);
 
-		if (zstream->zerr == Z_STREAM_ERROR)
-			return zstream_seterr(zstream);
+		if (zstream_seterr(zstream))
+			return -1;
 
 		out_used = (out_queued - zstream->z.avail_out);
 		out_remain -= out_used;