Inline Rename: Map caret position to correct buffer on Home/End

Fixes bug #2516 by mapping the new caret position to the correct buffer when Home/End is pressed during InlineRename. This change also avoids exceptions when we fail to map the selected spans down to our buffer when Inline Rename is invoked.

src/EditorFeatures/Core/Implementation/InlineRename/CommandHandlers/RenameCommandHandler_LineStartEndHandler.cs

@@ -92,16 +92,29 @@ private bool HandleLineStartOrLineEndCommand(ITextBuffer subjectBuffer, ITextVie
                         return false;
                     }
 
+                    // The PointTrackingMode should not matter because we are not tracking between
+                    // versions, and the PositionAffinity is set towards the identifier.
+                    var newPointInView = view.BufferGraph.MapUpToBuffer(
+                        newPoint,
+                        PointTrackingMode.Negative,
+                        lineStart ? PositionAffinity.Successor : PositionAffinity.Predecessor,
+                        view.TextBuffer);
+
+                    if (!newPointInView.HasValue)
+                    {
+                        return false;
+                    }
+
                     if (extendSelection)
                     {
-                        view.Selection.Select(view.Selection.AnchorPoint, new VirtualSnapshotPoint(newPoint));
+                        view.Selection.Select(view.Selection.AnchorPoint, new VirtualSnapshotPoint(newPointInView.Value));
                     }
                     else
                     {
                         view.Selection.Clear();
                     }
 
-                    view.Caret.MoveTo(newPoint);
+                    view.Caret.MoveTo(newPointInView.Value);
                     return true;
                 }
             }

src/EditorFeatures/Core/Implementation/InlineRename/CommandHandlers/RenameCommandHandler_RenameHandler.cs

@@ -91,7 +91,8 @@ private void ExecuteRenameWorker(RenameCommandArgs args, CancellationToken cance
             var selectedSpans = args.TextView.Selection.GetSnapshotSpansOnBuffer(args.SubjectBuffer);
 
             // Now make sure the entire selection is contained within that token.
-            if (selectedSpans.Count > 1)
+            // There can be zero selectedSpans in projection scenarios.
+            if (selectedSpans.Count != 1)
             {
                 ShowErrorDialog(workspace, EditorFeaturesResources.YouMustRenameAnIdentifier);
                 return;