Initialize stashbase even stash_max_blocks = 0

Change-Id: I480c02ffedd811f4dda9940ef979a05ff54f1435
Bug: 19410117
diff --git a/updater/blockimg.c b/updater/blockimg.c
index a0f81e9..9c39634 100644
--- a/updater/blockimg.c
+++ b/updater/blockimg.c
@@ -1643,7 +1643,7 @@
             goto pbiudone;
         }
 
-        if (stash_max_blocks > 0) {
+        if (stash_max_blocks >= 0) {
             res = CreateStash(state, stash_max_blocks, blockdev_filename->data,
                     &params.stashbase);