fix fillRegion/clearRegion.

lib/widget.js

@@ -1752,6 +1752,9 @@ Screen.prototype.fillRegion = function(attr, ch, xi, xl, yi, yl, override) {
     , cell
     , xx;
 
+  if (xi < 0) xi = 0;
+  if (yi < 0) yi = 0;
+
   for (; yi < yl; yi++) {
     if (!lines[yi]) break;
     for (xx = xi; xx < xl; xx++) {

test/widget.js

@@ -321,7 +321,7 @@ setInterval(function() {
     progress.reset();
   }
   progress.progress(2);
+  progress.atop -= 2;
   screen.render();
   setTimeout(fill, 300);
-  progress.atop -= 2;
 })();