Fix memory leak in process_case_item().

systemverilog-plugin/UhdmAst.cc

diff --git a/systemverilog-plugin/UhdmAst.cc b/systemverilog-plugin/UhdmAst.cc
index dcf9757..36c5080 100644
--- a/systemverilog-plugin/UhdmAst.cc
+++ b/systemverilog-plugin/UhdmAst.cc
@@ -4201,8 +4201,7 @@
                 current_node->children.push_back(node);
             }
         }
-        // FIXME: If we release the handle here, visiting vpiStmt fails for some reason
-        // vpi_release_handle(expr_h);
+        vpi_release_handle(expr_h);
     }
     vpi_release_handle(itr);
     if (current_node->children.empty()) {