Merge 132848 - IndexedDB: Crash on checking version of corrupt backing store

Merge 132848 - IndexedDB: Crash on checking version of corrupt backing store
https://bugs.webkit.org/show_bug.cgi?id=100692

Reviewed by Tony Chang.

If the backing store fails to open (due to corruption, non-writeable disk, etc)
the subsequent schema version check dereferences a null pointer. Fix to only
do the schema check if the database opened.

Chromium tests will be included with crrev.com/11196029

* Modules/indexeddb/IDBLevelDBBackingStore.cpp:
(WebCore::IDBLevelDBBackingStore::open):


TBR=jsbell@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=133043