Fix null reference in debugger (#3517)

libraries/Microsoft.Bot.Builder.Dialogs.Debugging/DebuggerSourceMap.cs

@@ -228,7 +228,7 @@ namespace Microsoft.Bot.Builder.Dialogs.Debugging
                 options = from sourceItem in sourceByItem
                           let source = sourceItem.Value
                           where PathEquals(source.Path, row.Source.Path)
-                          where source.StartPoint.LineIndex <= row.SourceBreakpoint.Line && source.EndPoint.LineIndex >= row.SourceBreakpoint.Line
+                          where source.StartPoint?.LineIndex <= row.SourceBreakpoint.Line && source.EndPoint?.LineIndex >= row.SourceBreakpoint.Line
                           let distance = row.SourceBreakpoint.Line - source.StartPoint.LineIndex
                           orderby distance
                           select sourceItem;

tests/Microsoft.Bot.Builder.TestBot.Json/.vscode/launch.json

@@ -18,9 +18,8 @@
             "args": [
                 "run",
                 "--no-build",
-                "--",
-                "--debugport",
-                "0"
+                "--root",
+                "${workspaceFolder}/Samples"
             ]
         },
         {