Stress part has bug when using LIBXC

[dyzheng]

Describe the bug

In case "tests/integrate/101_PW_15_f_pseudopots"

The result of stress of "dft_functional pbe" is -141.8148867733 The result of stress of "dft_functional GGA_X_PBE+GGA_C_PBE" is -191476.1078066163

Expected behavior

No response

To Reproduce

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Environment

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Additional Context

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[jinzx10]

probably results from a missing term (rho_core) in convert_vtxc_v (0.5 should be replaced by "1/nspin0" in production code):

check QE, PW/src/gradcorr.f90 for details.