Added debugging check on line 1604

I added the code assert(f->valid_bits >= n);  instead of removing if (f->valid_bits < 0) return 0; to improve code with checking and debugging instead.

stb_vorbis.c

@@ -1601,6 +1601,8 @@ static uint32 get_bits(vorb *f, int n)
       }
    }
 
+   assert(f->valid_bits >= n);
+   
    z = f->acc & ((1 << n)-1);
    f->acc >>= n;
    f->valid_bits -= n;