fixed NullReferenceException in Profiler/FindReferences, when trying to search for unresolved/non-user code

src/AddIns/Analysis/Profiler/Frontend/AddIn/Src/Commands/FindReferences.cs

@@ -19,10 +19,19 @@ namespace ICSharpCode.Profiler.AddIn.Commands
 		{
 			var selectedItem = GetSelectedItems().FirstOrDefault();
 
-			if (selectedItem != null) {
+			if (selectedItem == null)
+				return;
+			
 			IClass c = GetClassFromName(selectedItem.FullyQualifiedClassName);
-				if (c != null) {
+			
+			if (c == null)
+				return;
+			
 			IMember member = GetMemberFromName(c, selectedItem.MethodName, selectedItem.Parameters);
+			
+			if (member == null)
+				return;
+			
 			string memberName = member.DeclaringType.Name + "." + member.Name;
 			using (AsynchronousWaitDialog monitor = AsynchronousWaitDialog.ShowWaitDialog("${res:SharpDevelop.Refactoring.FindReferences}"))
 			{
@@ -32,6 +41,4 @@ namespace ICSharpCode.Profiler.AddIn.Commands
 			}
 		}
 	}
-		}
-	}
 }