Unused variable and generally suspicious code in `bloaty.cc`

Compiling raises a "variable set but not used" warning for `filtered` in `bloaty.cc` here:
https://github.com/google/bloaty/blob/073e01d04fc06d64eeb5cdb9adeae035a34e4b13/src/bloaty.cc#L828-L854
But also, `file_filtered` and `vm_filtered` are initialized to 0, and then never updated... so the condition on line 838 is always true, and everything below is dead code? I'm not sure if I'm missing something. I'm not familiar with bloaty internals, so I'm not sure what the right fix is, but just wanted to let you know about this.