fixing races in 2 test cases

[sanji-programmer]

Hi,

I noticed the both test cases failed sometimes (see below). After some investigation, I noticed that the function ensureIndex is not sync (as stated in the comment) and some operations may races with the assertions. The changes seemed to solve the race as I ran the test cases several times with no error.

1) Database
       Using indexes
         ensureIndex and index initialization in database loading
           ensureIndex can be called before a loadDatabase and still be initialized and filled correctly:

      Uncaught AssertionError: expected 0 to equal 3
      + expected - actual

      -0
      +3

  1 failing

  1) Database
       Using indexes
         ensureIndex and index initialization in database loading
           If a unique constraint is not respected, database loading will not work and no data will be inserted:
     Uncaught TypeError: Cannot read property 'should' of undefined

I posted a issue #609 to update the documentation of the function.