do not set variable value if it did not change

fixes #12885

src/vs/workbench/parts/debug/electron-browser/debugViewer.ts

@@ -119,7 +119,7 @@ function renderRenameBox(debugService: debug.IDebugService, contextViewService:
 				debugService.removeFunctionBreakpoints(element.getId()).done(null, errors.onUnexpectedError);
 			} else if (element instanceof model.Variable) {
 				(<model.Variable>element).errorMessage = null;
-				if (renamed) {
+				if (renamed && element.value !== inputBox.value) {
 					debugService.setVariable(element, inputBox.value)
 						// if everything went fine we need to refresh that tree element since his value updated
 						.done(() => tree.refresh(element, false), errors.onUnexpectedError);