Altium PCB: improve default textbox alignment when isJustificationValid flag is not set.

While there is an example where the default text frame justification is center-center,
in other cases it should be left-bottom, but we don't know what controls this yet.

An example where text frames should be imported with center-center justification:
https://github.com/FpgaDigital/RK3328/blob/830d51b80c77aba6c7570d273521770dfeeee0f9/RK3328.PcbDoc

But in "mb1897-bdp.zip" from #18784
text frames should use left-bottom justification.