page 2x2 - generates 4 same pages - https://github.com/esteinberg/plantuml4idea/issues/171
SourceStringReader#getBlocks returns one block with 4 NBimages. So I am calling #outputImage for those 4 pages and getting the same one.
I checked that PngSplitter is only called via PSystemUtils#exportDiagrams, which I cannot use.
Also, btw is there any case when there is more than 1 block? I assume that there is only one per @start-@end tag pair...