Small improvement to go/unhandled-writable-file-close

Author: owen-mc

go/ql/src/InconsistentCode/UnhandledCloseWritableHandle.ql

@@ -70,8 +70,8 @@ predicate unhandledCall(DataFlow::CallNode call) {
  */
 predicate isWritableFileHandle(DataFlow::Node source, DataFlow::CallNode call) {
   exists(OpenFileFun f, DataFlow::Node flags, QualifiedName flag |
-    // check that the source is a result of the call
-    source = call.getAResult() and
+    // check that the source is the first result of the call
+    source = call.getResult(0) and
     // find a call to the os.OpenFile function
     f.getACall() = call and
     // get the flags expression used for opening the file