``Insert.add_auto_attribs`` breaks multi-line attributes.

[gswifort]

Describe the bug I have defined a block with a multi-line attribute. After inserting a reference to the block and calling .add_auto_attribs() the multi-line attributes change to single-line.

To Reproduce Version1.3.4

import ezdxf


def main():
    doc = ezdxf.readfile("test.dxf")
    print(doc.dxfversion)  # AC1032
    msp = doc.modelspace()
    obj = msp.add_blockref("TEST", (0, 0))
    obj.add_auto_attribs({"ATTR": "10"})
    doc.saveas("test2.dxf")


if __name__ == "__main__":
    main()

Screenshots

• test.dxf
• test2.dxf