Fix #117318: Empty Defocus output when max blur is less than 1

The Defocus node produces an empty output when the max blur is less than
1. This patch fixes that by passing the image through in that case,
since it is identity in this case.

source/blender/nodes/composite/nodes/node_composite_defocus.cc

@@ -108,7 +108,7 @@ class DefocusOperation : public NodeOperation {
   {
     Result &input = get_input("Image");
     Result &output = get_result("Image");
-    if (input.is_single_value()) {
+    if (input.is_single_value() || node_storage(bnode()).maxblur < 1.0f) {
       input.pass_through(output);
       return;
     }