remove push/pop/splice calls to BufferLine

src/Buffer.ts

@@ -124,9 +124,7 @@ export class Buffer implements IBuffer {
       if (this._terminal.cols < newCols) {
         const ch: CharData = [DEFAULT_ATTR, NULL_CELL_CHAR, NULL_CELL_WIDTH, NULL_CELL_CODE]; // does xterm use the default attr?
         for (let i = 0; i < this.lines.length; i++) {
-          while (this.lines.get(i).length < newCols) {
-            this.lines.get(i).push(ch);
-          }
+          this.lines.get(i).resize(newCols, ch);
         }
       }