defensive underline event coords handling in DOM renderer

Author: jerch

src/browser/renderer/dom/DomRenderer.ts

@@ -393,8 +393,18 @@ export class DomRenderer extends Disposable implements IRenderer {
   }
 
   private _setCellUnderline(x: number, x2: number, y: number, y2: number, cols: number, enabled: boolean): void {
-    x = this._cellToRowElements[y][x];
-    x2 = this._cellToRowElements[y2][x2];
+    const lenY = this._cellToRowElements.length - 1;
+    if (y < 0) x = 0;
+    if (y2 < 0) x2 = 0;
+    y = Math.max(Math.min(y, lenY), 0);
+    y2 = Math.max(Math.min(y2, lenY), 0);
+    const elemY = this._cellToRowElements[y];
+    const elemY2 = this._cellToRowElements[y2];
+    if (x >= elemY.length || x2 >= elemY2.length) {
+      return;
+    }
+    x = elemY[x];
+    x2 = elemY2[x2];
 
     if (x === -1 || x2 === -1) {
       return;