fix wrong position if selection end is at end of line

src/domcoords.js

@@ -234,12 +234,12 @@ function singleRect(object, bias) {
 // : (EditorView, number) → {left: number, top: number, right: number, bottom: number}
 // Given a position in the document model, get a bounding box of the
 // character at that position, relative to the window.
-export function coordsAtPos(view, pos) {
+export function coordsAtPos(view, pos, end = false) {
   let {node, offset} = view.docView.domFromPos(pos)
   let side, rect
   if (node.nodeType == 3) {
     if (offset < node.nodeValue.length) {
-      rect = singleRect(textRange(node, offset, offset + 1), -1)
+      rect = singleRect(textRange(node, offset, (end) ? 0 : offset + 1), -1)
       side = "left"
     }
     if ((!rect || rect.left == rect.right) && offset) {