[orca] Eliminate some redundant work we were doing handling text selection

[Joanmarie Diggs <joanied src gnome org>]

commit f3a3408388f69493250a8df0bba5a2b1eec7b9c3
Author: Joanmarie Diggs <jdiggs igalia com>
Date:   Fri Mar 13 15:08:37 2020 -0400

    Eliminate some redundant work we were doing handling text selection

 src/orca/scripts/web/script_utilities.py | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
---
diff --git a/src/orca/scripts/web/script_utilities.py b/src/orca/scripts/web/script_utilities.py
index 584ed952f..e9e15671f 100644
--- a/src/orca/scripts/web/script_utilities.py
+++ b/src/orca/scripts/web/script_utilities.py
@@ -1829,13 +1829,16 @@ class Utilities(script_utilities.Utilities):
         start, end = self._getSelectionAnchorAndFocus(obj)
         self._script.pointOfReference['selectionAnchorAndFocus'] = (start, end)
 
-        oldSubtree = self._getSubtree(oldStart, oldEnd)
-        newSubtree = self._getSubtree(start, end)
-
         def _cmp(obj1, obj2):
             return self.pathComparison(pyatspi.getPath(obj1), pyatspi.getPath(obj2))
 
-        descendants = sorted(set(oldSubtree).union(newSubtree), key=functools.cmp_to_key(_cmp))
+        oldSubtree = self._getSubtree(oldStart, oldEnd)
+        if start == oldStart and end == oldEnd:
+            descendants = oldSubtree
+        else:
+            newSubtree = self._getSubtree(start, end)
+            descendants = sorted(set(oldSubtree).union(newSubtree), key=functools.cmp_to_key(_cmp))
+
         for descendant in descendants:
             if descendant not in (oldStart, oldEnd, start, end) \
                and pyatspi.findAncestor(descendant, lambda x: x in descendants):