Fix having to create blank VImages for operations that should be static

[lopcode]

Relates to #128

Affected functions:

analyzeload, arrayjoin, bandjoin, bandrank, black, composite, csvload, csvloadSource, eye, fitsload, fitsloadSource, fractsurf, gaussmat, gaussnoise, gifload, gifloadBuffer, gifloadSource, grey, heifload, heifloadBuffer, heifloadSource, identity, jp2kload, jp2kloadBuffer, jp2kloadSource, jpegload, jpegloadBuffer, jpegloadSource, jxlload, jxlloadBuffer, jxlloadSource, logmat, magickload, magickloadBuffer, maskButterworth, maskButterworthBand, maskButterworthRing, maskFractal, maskGaussian, maskGaussianBand, maskGaussianRing, maskIdeal, maskIdealBand, maskIdealRing, matload, matrixload, matrixloadSource, openexrload, openslideload, openslideloadSource, pdfload, pdfloadBuffer, pdfloadSource, perlin, pngload, pngloadBuffer, pngloadSource, ppmload, ppmloadSource, radload, radloadBuffer, radloadSource, rawload, sdf, sines, sum, svgload, svgloadBuffer, svgloadSource, switch1, text, thumbnail, thumbnailBuffer, thumbnailSource, tiffload, tiffloadBuffer, tiffloadSource, tonelut, vipsload, vipsloadSource, webpload, webploadBuffer, webploadSource, worley, xyz, zone