fix possible NullReferenceExceptions in ResolveExtensionMethod; should fix http://usagedatacollector.sharpdevelop.net/analysis/ExceptionGroup/Edit/229

src/AddIns/Misc/SharpRefactoring/Project/Src/MenuItemFactories/ResolveExtensionMethod.cs

@@ -28,9 +28,14 @@ namespace SharpRefactoring
 				return null;
 			if (!(context.ResolveResult is UnknownMethodResolveResult))
 				return null;
+			if (context.ProjectContent == null)
+				return null;
 			
 			UnknownMethodResolveResult rr = context.ResolveResult as UnknownMethodResolveResult;
 			
+			if (rr.CallingClass == null)
+				return null;
+			
 			MenuItem item = new MenuItem() {
 				Header = string.Format(StringParser.Parse("${res:AddIns.SharpRefactoring.ResolveExtensionMethod}"), rr.CallName),
 				Icon = ClassBrowserIconService.GotoArrow.CreateImage()
@@ -38,11 +43,9 @@ namespace SharpRefactoring
 			
 			List<IClass> results = new List<IClass>();
 			
-			IProjectContent pc = rr.CallingClass.ProjectContent;
-			
-			SearchAllExtensionMethodsWithName(results, pc, rr.CallName);
+			SearchAllExtensionMethodsWithName(results, context.ProjectContent, rr.CallName);
 			
-			foreach (IProjectContent content in pc.ReferencedContents)
+			foreach (IProjectContent content in context.ProjectContent.ReferencedContents)
 				SearchAllExtensionMethodsWithName(results, content, rr.CallName);
 			
 			if (!results.Any())