Compositor: Fix log message about shadow pass

Fix a slightly messy log message about a pass not being a shadow pass,
where there was no end quote or space after the pass name.

simgear/scene/viewer/CompositorPass.cxx

@@ -226,7 +226,7 @@ PassBuilder::build(Compositor *compositor, const SGPropertyNode *root,
                         cullcb->getLightMatrixUniform());
                 } else {
                     SG_LOG(SG_INPUT, SG_WARN, "ScenePassBuilder::build: Pass '"
-                           << shadow_pass_name << "is not a shadow pass");
+                           << shadow_pass_name << "' is not a shadow pass");
                 }
             }
         }