New Pixmap from pixmap crashes interpreter for unsupported colorspace

[JorjMcKie]

If a pixmap pix0 has a colorspace unsupported by MuPDF (i.e. one generated from image files), trial to convert it with pix1 = fitz.Pixmap(my_cspace, pix0) will crash the Python interpreter.

This can e.g. occur when the image source contains only black & white with no alpha channel. Then pix0.n will equal 1.

Fix:

Check 2 <= pix0.n <= 5 and raise an exception otherwise. This has been tested already and will soon be uploaded.

Circumvention:

Amazingly, pix0.writePNG(...) and pix0.getPNGData() will still both work in such situations! So, whenever pix0.n is not in valid range, do pix00 = fitz.Pixmap(pix0.getPNGData()) and then do pix1 = fitz.Pixmap(my_cspace, pix00)