Print better failure message

[eigenwillig]

When |Flooding_Layer|0 is missing, the program is just failing. Instead it should detect such a mistake!

TypeError: Cannot read property 'trim' of undefined
    at rp.then (/usr/lib/node_modules/agsout/index.js:70:49)
    at tryCatcher (/usr/lib/node_modules/agsout/node_modules/bluebird/js/release/util.js:16:23)
    at Promise._settlePromiseFromHandler (/usr/lib/node_modules/agsout/node_modules/bluebird/js/release/promise.js:512:31)
    at Promise._settlePromise (/usr/lib/node_modules/agsout/node_modules/bluebird/js/release/promise.js:569:18)
    at Promise._settlePromise0 (/usr/lib/node_modules/agsout/node_modules/bluebird/js/release/promise.js:614:10)
    at Promise._settlePromises (/usr/lib/node_modules/agsout/node_modules/bluebird/js/release/promise.js:693:18)
    at Async._drainQueue (/usr/lib/node_modules/agsout/node_modules/bluebird/js/release/async.js:133:16)
    at Async._drainQueues (/usr/lib/node_modules/agsout/node_modules/bluebird/js/release/async.js:143:10)
    at Immediate.Async.drainQueues (/usr/lib/node_modules/agsout/node_modules/bluebird/js/release/async.js:17:14)
    at runCallback (timers.js:794:20)
    at tryOnImmediate (timers.js:752:5)
    at processImmediate [as _immediateCallback] (timers.js:729:5)