Icon: Make png2ico / windres failure non-fatal

cmake/modules/AddAppIconMacro.cmake

@@ -66,7 +66,7 @@ macro (KDE4_ADD_APP_ICON appsources pattern)
                 message(STATUS "Unable to find a related icon that matches pattern ${pattern} for variable ${appsources} - application will not have an application icon!")
             endif(_icons)
         else(PNG2ICO_EXECUTABLE AND WINDRES_EXECUTABLE)
-            message(FATAL_ERROR "Unable to find the png2ico or windres utilities - application will not have an application icon!")
+            message(WARNING "Unable to find the png2ico or windres utilities - application will not have an application icon!")
         endif(PNG2ICO_EXECUTABLE AND WINDRES_EXECUTABLE)
     endif(WIN32)
     if (APPLE)