Tightened icon and cursor file detection heuristics.

Tightened icon and cursor file detection heuristics.

When loading a TGA file that has an image type of uncompressed true colour it would be falsely detected as a cursor file and as an icon file if type is of uncompressed colour mapped. Lower the chance of this happening by also checking the remaining member of an ICO and CUR header which represents the number of images in the file. This member has to be non-zero (checked against all found ICO and CUR files in an XP installation).

See also #12702.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66491 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775