Merge pull request #1399 from Microsoft/checkSymbolExists

Check if the symbol exists before checking its visibility in isEntityNameVisible.

Author: DanielRosenwasser

src/compiler/checker.ts

@@ -1012,7 +1012,7 @@ module ts {
             var symbol = resolveName(enclosingDeclaration, (<Identifier>firstIdentifier).text, meaning, /*nodeNotFoundErrorMessage*/ undefined, /*nameArg*/ undefined);
 
             // Verify if the symbol is accessible
-            return hasVisibleDeclarations(symbol) || <SymbolVisibilityResult>{
+            return (symbol && hasVisibleDeclarations(symbol)) || <SymbolVisibilityResult>{
                 accessibility: SymbolAccessibility.NotAccessible,
                 errorSymbolName: getTextOfNode(firstIdentifier),
                 errorNode: firstIdentifier