Fix handling of failed shared data map creation in overlay.

createSharedDataMap can fail to map the shared data used by other
functionality in the overlay dll. In this case pointers including
"sd" remain NULLd. With the recent overlay changes the modified
shared data structures changed, triggering this case when running
different versions. This crashed Mumble on startup due to an
unchecked dereference of the "sd" pointer.

Also when extracting createSharedDataMap during refactoring behavior
was changed. The overlay kept injecting itself even if the mapping
failed. This also addresses this by making createSharedDataMap return
a bool indicating success or failure.
Russian translation fixes