FileRequest: Fix transfer error detection not working. CID 1162764
trim support code: The passed in MemoryDeleter was never used.

When a buffer has to be allocated, I guess the intention was to
assign the MemoryDeleter to it, so that it would later be freed.
CID 1130505
HaikuDepot: Initialize fMainWindow in App. CID 1108452
HaikuDepot: Prevent future oversight...

... and init fSpanStartOffset. CID 1108437