snippets - fix leaking listeners that break subsequent snippet insertion

src/vs/editor/contrib/snippet/browser/snippetController2.ts

@@ -62,12 +62,16 @@ export class SnippetController2 {
 		if (!this._snippet) {
 			// create a new session
 			this._snippet = new SnippetSession(this._editor);
+			this._snippet.insert(template, overwriteBefore, overwriteAfter);
+			this._snippetListener = [
+				this._editor.onDidChangeModel(() => this.cancel()),
+				this._editor.onDidChangeCursorSelection(() => this._updateState())
+			];
+		} else {
+			// only insert the snippet when a session
+			// is already active
+			this._snippet.insert(template, overwriteBefore, overwriteAfter);
 		}
-		this._snippet.insert(template, overwriteBefore, overwriteAfter);
-		this._snippetListener = [
-			this._editor.onDidChangeModel(() => this.cancel()),
-			this._editor.onDidChangeCursorSelection(() => this._updateState())
-		];
 		if (undoStopAfter) {
 			this._editor.getModel().pushStackElement();
 		}