Fix case when position === 0

(cherry picked from commit 1231c9e145)

src/services/services.ts

@@ -5490,7 +5490,7 @@ namespace ts {
 
                     const nameTable = getNameTable(sourceFile);
 
-                    if (lookUp(nameTable, internedName)) {
+                    if (lookUp(nameTable, internedName) !== undefined) {
                         result = result || [];
                         getReferencesInNode(sourceFile, symbol, declaredName, node, searchMeaning, findInStrings, findInComments, result, symbolToIndex);
                     }