TASK: Provide proper error message when no request handler can be resolved
TASK: Provide proper error message when no request handler can be resolved

Previously Flow would just fail with an error message:
`Warning: ksort() expects parameter 1 to be array, null given`
when for some reason no suitable request handler can be found for the current request.
This change will instead throw a useful exception and hint the user at a setup problem.

kdambekalns/flow-development-collection,gerhard-boden/flow-development-collection,aertmann/flow-development-collection,dlubitz/flow-development-collection,albe/flow-development-collection,robertlemke/flow-development-collection,chewbakartik/flow-development-collection,daniellienert/flow-development-collection,fcool/flow-development-collection,neos/flow-development-collection,bwaidelich/flow-development-collection,albe/flow-development-collection,mkeitsch/flow-development-collection,neos/flow-development-collection,robertlemke/flow-development-collection,neos/flow-development-collection,chewbakartik/flow-development-collection,neos/flow-development-collection,daniellienert/flow-development-collection,robertlemke/flow-development-collection,robertlemke/flow-development-collection,albe/flow-development-collection,aertmann/flow-development-collection,kitsunet/flow-development-collection,fcool/flow-development-collection,daniellienert/flow-development-collection,fcool/flow-development-collection,chewbakartik/flow-development-collection,kdambekalns/flow-development-collection,kdambekalns/flow-development-collection,mkeitsch/flow-development-collection,dlubitz/flow-development-collection,kitsunet/flow-development-collection,gerhard-boden/flow-development-collection,bwaidelich/flow-development-collection,mkeitsch/flow-development-collection,kdambekalns/flow-development-collection,gerhard-boden/flow-development-collection,aertmann/flow-development-collection,kitsunet/flow-development-collection,dlubitz/flow-development-collection,bwaidelich/flow-development-collection,fcool/flow-development-collection