[sql] Fix leafCursorCellDecode() crash.

If sqlite_master lists a valid root page for the table, and the root
page is an interior b-tree page, and none of the children are valid
pages, then recoverOpen() gets to leafCursorCreate(), and:
 - leafCursorLoadPage() loads the page as an interior node into a parent
   of the leaf cursor.
 - leafCursorNextPage() returns SQLITE_DONE because no more pages are
   available.
 - SQLITE_OK is returned, but pCursor->pPage is left empty.
Then recoverFilter() calls leafCursorCellDecode(), which attempts to
access pCursor->pPage->pgno, where pPage is NULL and pgno is at offset
12, causing a crash accessing 0x0000000c.

The fix handles this by using bEOF to signal no data.  This matches what
would happen if there were valid leaf pages which contained no valid
rows (recoverFilter() would call recoverNext() which would see
SQLITE_DONE from leafCursorNextValidCall(), set bEOF, and return
SQLITE_OK).

Reverts r241341, a diagnostic which is no longer necessary.

BUG=326646,329302
TBR=michaeln@chromium.org

Review URL: https://codereview.chromium.org/116853004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242701 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242701