fixes #236 CellBuffer.Fill doesn't set cell.width

cell.go

@@ -179,12 +179,13 @@ func (cb *CellBuffer) Resize(w, h int) {
 
 // Fill fills the entire cell buffer array with the specified character
 // and style.  Normally choose ' ' to clear the screen.  This API doesn't
-// support combining characters.
+// support combining characters, or characters with a width larger than one.
 func (cb *CellBuffer) Fill(r rune, style Style) {
 	for i := range cb.cells {
 		c := &cb.cells[i]
 		c.currMain = r
 		c.currComb = nil
 		c.currStyle = style
+		c.width = 1
 	}
 }