Check if there is an edit before applying it to the buffer (microsoft…

…#170301)

This was throwing an error before if you were writing `undefined` to a property that didn't exist.

Fixes microsoft#168092

src/vs/workbench/services/configuration/common/jsonEditingService.ts

@@ -51,7 +51,7 @@ export class JSONEditingService implements IJSONEditingService {
 		let hasEdits: boolean = false;
 		for (const value of values) {
 			const edit = this.getEdits(model, value)[0];
-			hasEdits = this.applyEditsToBuffer(edit, model);
+			hasEdits = !!edit && this.applyEditsToBuffer(edit, model);
 		}
 		if (hasEdits) {
 			return this.textFileService.save(model.uri);