Fixed null reference exception in WriteableProjectEvaluator if a null IProject is returned from the ProjectService.CurrentProject.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/branches/3.0@3808 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/Main/Base/Project/Src/Internal/ConditionEvaluators/WriteableProjectEvaluator.cs

@@ -20,7 +20,7 @@ namespace ICSharpCode.SharpDevelop
 		public bool IsValid(object caller, Condition condition)
 		{
 			IProject project = (caller as IProject) ?? ProjectService.CurrentProject;
-			return !project.ReadOnly;
+			return project != null && !project.ReadOnly;
 		}
 	}
 }