Silence a valgrind warning caused by zlib:

==31182== Conditional jump or move depends on uninitialised value(s)
==31182==    at 0xA9188B: longest_match (deflate.c:1143)
==31182==    by 0xA92C19: deflate_slow (deflate.c:1595)
==31182==    by 0xA90C6B: deflate (deflate.c:790)
==31182==    by 0x9B447B: page_zip_compress (page0zip.c:1342)
==31182==    by 0x9A8540: page_cur_insert_rec_zip_reorg (page0cur.c:1174)
==31182==    by 0x9A8998: page_cur_insert_rec_zip (page0cur.c:1279)
==31182==    by 0x9214F9: page_cur_tuple_insert (page0cur.ic:264)
==31182==    by 0x9221A2: btr_cur_optimistic_insert (btr0cur.c:1314)
==31182==    by 0x9C99EB: row_ins_index_entry_low (row0ins.c:2087)
==31182==    by 0x9C9DFB: row_ins_index_entry (row0ins.c:2167)
==31182==    by 0x9CA057: row_ins_index_entry_step (row0ins.c:2252)
==31182==    by 0x9CA0FD: row_ins (row0ins.c:2384)
==31182==    by 0x9CA760: row_ins_step (row0ins.c:2494)
==31182==    by 0x8CBF7E: row_insert_for_mysql (row0mysql.c:1138)
==31182==    by 0x8BCF32: ha_innobase::write_row(unsigned char*) (ha_innodb.cc:4929)
==31182==    by 0x736E03: handler::ha_write_row(unsigned char*) (handler.cc:4682)

mysql-test/valgrind.supp

@@ -174,7 +174,7 @@
 }
 
 {
-   libz longest_match called from InnoDB
+   libz longest_match called from btr_store_big_rec_extern_fields
    Memcheck:Cond
    fun:longest_match
    fun:deflate_slow
@@ -182,6 +182,15 @@
    fun:btr_store_big_rec_extern_fields
 }
 
+{
+   libz longest_match called from page_zip_compress
+   Memcheck:Cond
+   fun:longest_match
+   fun:deflate_slow
+   fun:deflate
+   fun:page_zip_compress
+}
+
 {
    libz longest_match2
    Memcheck:Cond