Function fz_morph_error 

pub unsafe extern "C" fn fz_morph_error(
    ctx: *mut fz_context,
    fromcode: c_int,
    tocode: c_int,
)

Called within a catch block this modifies the current
exception’s code. If it’s of type ‘fromcode’ it is
modified to ‘tocode’. Typically used for ‘downgrading’
exception severity.