Better diagnostics for easily detectable developer errors in QueryUrisLoader

[ahwitz]

Hey! At this point in QueryUrisLoader, there's a try/catch that prints additional diagnostics for when the first item returned isn't an integer. There were two other cases where I got an empty NullPointerException with no diagnostics that should be pretty easy to detect:

• No array is returned by getUris
• A JS array (without a wrapping xdmp.arrayValues call) is returned by the module

Only asking because there's already developer error diagnostics there, and I had to dig back into the code from the stack trace to figure out what might be going wrong. Would it be possible/worthwhile to add two more NullPointer catches there to help out future developers who run into similar mistakes?