Patch for issue #238: Check if primary ID column is available before try...

...ing to access it in the cursor.
(like Model.loadFromCursor())

I have not written a test for that situation, as I am pretty new to Java and Android and far from having figured out everything :).
Hope someone with more experience in writing tests could add an appropriate test case to the test suite.


Greetz,
Florian

PS: I hope I am able to deliver a proper first pull request (appart from the missing test case) :)