Fix getVisualSelection() when called from visual mode

Adapted from here:
  https://stackoverflow.com/a/47051271/301717

plugin/Highlight.vim

@@ -1199,8 +1199,17 @@ function s:getVisualSelection()
     " https://stackoverflow.com/questions/1533565/how-to-get-visually-selected-text-in-vimscript
     "
     " Why is this not a built-in Vim script function?!
-    let [line_start, column_start] = getpos("'<")[1:2]
-    let [line_end, column_end] = getpos("'>")[1:2]
+    if mode() == "v"
+        let [line_start, column_start] = getpos("v")[1:2]
+        let [line_end, column_end] = getpos(".")[1:2]
+    else
+        let [line_start, column_start] = getpos("'<")[1:2]
+        let [line_end, column_end] = getpos("'>")[1:2]
+    end
+    if (line2byte(line_start) + column_start) > (line2byte(line_end) + column_end)
+        let [line_start, column_start, line_end, column_end] =
+        \   [line_end, column_end, line_start, column_start]
+    end
     let lines = getline(line_start, line_end)
     if len(lines) == 0
         return ''