Fix clear function when buffer is <= rows

src/xterm.js

@@ -3062,10 +3062,10 @@ Terminal.prototype.clear = function() {
     // Don't clear if it's already clear
     return;
   }
+  this.lines = [this.lines[this.ybase + this.y]];
   this.ydisp = 0;
   this.ybase = 0;
   this.y = 0;
-  this.lines = [this.lines[this.lines.length - 1]];
   for (var i = 1; i < this.rows; i++) {
     this.lines.push(this.blankLine());
   }