Fixed crash when saving as a monochrome TIFF image with incomplete options set.

Fixed crash when saving as a monochrome TIFF image with incomplete options set.

When setting only wxIMAGE_OPTION_TIFF_BITSPERSAMPLE to 1 the used samples per pixel (wxIMAGE_OPTION_TIFF_SAMPLESPERPIXEL) would still be set to 3. This is invalid and confuses libtiff, resulting in a crash ("possible heap corruption" during _TIFFfree using WinXP+MSVC8). Set the used samples per pixel to 1 explicitly in cases where only bits per sample is set to 1. Added a unit test to check for this problem (and verify the bits per sample from the saved image is indeed 1).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68782 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775