Validation in the date range option in PDF export

[dbarashev]

PDF export allows for choosing a date range for the chart image export. It is possible to define a range where the start date is after the end date. Apparently, this won't affect PDF export (there is only a task table image with no chart in the PDF file) but leads to crashes in the HTML export:

Caused by: java.lang.IllegalArgumentException: Width (0) and height (793) must be > 0
	at java.desktop/java.awt.image.SampleModel.<init>(SampleModel.java:127)
	at java.desktop/java.awt.image.SinglePixelPackedSampleModel.<init>(SinglePixelPackedSampleModel.java:144)
	at java.desktop/java.awt.image.SinglePixelPackedSampleModel.<init>(SinglePixelPackedSampleModel.java:110)
	at java.desktop/java.awt.image.PackedColorModel.createCompatibleSampleModel(PackedColorModel.java:312)
	at net.sourceforge.ganttproject.chart.export.RenderedChartImage.<init>(RenderedChartImage.java:51)
	at net.sourceforge.ganttproject.chart.ChartRasterImageBuilder.acceptChart(PrintChartApiImpl.kt:103)
	at net.sourceforge.ganttproject.chart.export.ChartImageBuilder.buildImage(ChartImageBuilder.kt:56)
	at net.sourceforge.ganttproject.chart.PrintChartApiImpl.buildImage(PrintChartApiImpl.kt:55)
	at net.sourceforge.ganttproject.chart.PrintChartApiImpl.exportChart(PrintChartApiImpl.kt:49)
	at org.ganttproject.impex.htmlpdf.ExporterToHTML$1.run(ExporterToHTML.java:87)
	at net.sourceforge.ganttproject.export.ExporterBase$2.run(ExporterBase.java:180)
	... 2 more