f2fs: advance index and offset after zeroing in large folio read

f2fs: advance index and offset after zeroing in large folio read

In f2fs_read_data_large_folio(), the block zeroing path calls
folio_zero_range() and then continues the loop. However, it fails to
advance index and offset before continuing.

This can cause the loop to repeatedly process the same subpage of the
folio, leading to stalls/hangs and incorrect progress when reading large
folios with holes/zeroed blocks.

Fix it by advancing index and offset unconditionally in the loop
iteration, so they are updated even when the zeroing path continues.

Signed-off-by: Nanzhe Zhao <nzzhao@126.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>