2.0.2-beta: Fix for handling in case of multiple mounts / paths

An attempt in fixing this issue winnfsd/issues/13
The server was crashing when you had two path mappings and you tried to mount both of them.
It looks like there was no handling in place to actually figure out which path mapping has to be used for the mounted path.
This ultimately led to unhandled errors.
The patched version is more defensive when using the currently selected path mapping and if it doesn't fit it searches a fitting path mapping for the mounted path.