checkplot.twolsp_checkplot_png: don't break if bestperiodhighlight is None
checkplot.twolsp_checkplot_png: don't break if bestperiodhighlight is None

waqasbhatti/astrobase,waqasbhatti/astrobase,lgbouma/astrobase,lgbouma/astrobase,waqasbhatti/astrobase,lgbouma/astrobase