Handle null corpId, accountKey, buy and sell values

Some rare scenario's come up when there are buy orders on a wallet but no sell orders or potentially even vice versa.  I believe this is what the original union tried to solve (with its right join) but when it does return a result, it returns a result with a null corp id and null account key.  These nulls don't make it into the summary table on the resulting page :(.
Merge pull request #1 from maurerit/master

Handle null corpId, accountKey, buy and sell values