[BUG] Read qe/cp/traj with unit angstrom without .cel file

[LavendaRaphael]

Summary

When dpdata read 'qe/cp/traj' with unit angstrom without '.cel' file, it will generate wrong result.

dpdata 0.2.6

Steps to Reproduce

Files list without cp.cel

cp.in
cp.pos

cp.in

...
CELL_PARAMETERS { angstrom }
       19.7299995422         0.0000000000         0.0000000000
        0.0000000000        19.7299995422         0.0000000000
        0.0000000000         0.0000000000        19.7299995422
...

command

dp_sys = dpdata.System(
    file_name = 'cp',
    fmt = 'qe/cp/traj',
    )
print(dp_sys['cells'][0])

output

[[10.44066613  0.          0.        ]
 [ 0.         10.44066613  0.        ]
 [ 0.          0.         10.44066613]]

When I add cp.cel file in filelist, then the output was right

cp.in
cp.pos
cp.cel

[[19.72999963  0.          0.        ]
 [ 0.         19.72999963  0.        ]
 [ 0.          0.         19.72999963]]

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