fix badcase for empty files

雾聪

2023-06-25 57558b4a7df571dd74dc1e23b694a23bb63249f4

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p m    p.m.
pm    p.m.
p.m.
p.m    p.m.
am    a.m.
a.m.
a.m    a.m.
a m    a.m.