document that CanRead() and GetImageCount() functions of wxImageHandlers do NOT modify the current stream position and that they require seekable streams; rename current GetImageCount() functions to DoGetImageCount() and put save-and-restore stream position logic in GetImageCount(); add comments in the various DoCanRead() and in DoGetImageCount() where the stream position is modified; remove unneeded SeekI(0) calls from DoCanRead() and DoGetImageCount() functions: they didn't allow to load images from non-seekable streams; implement forward-seeking in wxInputStream::SeekI() also for non-seekable streams

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@60852 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/imagpnm.cpp

@@ -180,6 +180,7 @@ bool wxPNMHandler::DoCanRead( wxInputStream& stream )
 {
     Skip_Comment(stream);
 
+    // it's ok to modify the stream position here
     if ( stream.GetC() == 'P' )
     {
         switch ( stream.GetC() )