Fix T67358: Compositor Disabled Node Config -> SegFault

The issue was caused by wrong conversion happening after some of the
proxies are removed. Easiest solution is to first remove proxies and
then add required converter operations.

Thanks Jeroen for the review!

source/blender/compositor/intern/COM_NodeOperationBuilder.cpp

@@ -98,10 +98,10 @@ void NodeOperationBuilder::convertToOperations(ExecutionSystem *system)
 
   add_operation_input_constants();
 
-  add_datatype_conversions();
-
   resolve_proxies();
 
+  add_datatype_conversions();
+
   determineResolutions();
 
   /* surround complex ops with read/write buffer */