Resize saved cursor position on buffer resize

Saved cursor coordinates were not being resized as well which could
lead to crashes when resizing down while the alt buffer is active.

Fixes #1151

src/Buffer.ts

@@ -177,16 +177,13 @@ export class Buffer implements IBuffer {
       }
 
       // Make sure that the cursor stays on screen
-      if (this.y >= newRows) {
-        this.y = newRows - 1;
-      }
+      this.x = Math.min(this.x, newCols - 1);
+      this.y = Math.min(this.y, newRows - 1);
       if (addToY) {
         this.y += addToY;
       }
-
-      if (this.x >= newCols) {
-        this.x = newCols - 1;
-      }
+      this.savedY = Math.min(this.savedY, newRows - 1);
+      this.savedX = Math.min(this.savedX, newCols - 1);
 
       this.scrollTop = 0;
     }