erofs: get correct count for unmapped range in fscache mode

For unmapped range, the returned map.m_llen is zero, and thus the
calculated count is unexpected zero.

Prior to the refactoring introduced by commit 1ae9470c3e14 ("erofs:
clean up .read_folio() and .readahead() in fscache mode"), only the
readahead routine suffers from this. With the refactoring of making
.read_folio() and .readahead() calling one common routine, both
read_folio and readahead have this issue now.

Fix this by calculating count separately in unmapped condition.

Fixes: c665b394b9e8 ("erofs: implement fscache-based data readahead")
Fixes: 1ae9470c3e14 ("erofs: clean up .read_folio() and .readahead() in fscache mode")
Signed-off-by: Jingbo Xu <[email protected]>
Reviewed-by: Gao Xiang <[email protected]>
Reviewed-by: Chao Yu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Gao Xiang <[email protected]>

0 files changed, 0 insertions, 0 deletions