accept grey PNM images (patch 1285885)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@35463 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/imagpnm.cpp

@@ -174,8 +174,10 @@ bool wxPNMHandler::DoCanRead( wxInputStream& stream )
     {
         switch ( stream.GetC() )
         {
-            case '3':
+            case '2': // ASCII Grey
-            case '6':
+            case '3': // ASCII RGB
+            case '5': // RAW Grey
+            case '6': // RAW RGB
                 return true;
         }
     }