Reset native scrollbar when hiding it

To avoid it reinitializing in a scrolled position on Chrome Issue codemirror#6819

Author: marijnh

src/display/scrollbars.js

@@ -60,6 +60,7 @@ class NativeScrollbars {
  this.vert.firstChild.style.height =
  Math.max(0, measure.scrollHeight - measure.clientHeight + totalHeight) + "px"
  } else {
+ this.vert.scrollTop = 0
  this.vert.style.display = ""
  this.vert.firstChild.style.height = "0"
  }