Removes fileno check to prevent valgrind error

Explicitly makes the fileptr null when close source is called
on a temporary file. This avoids a valgrind error.

Change-Id: I9c364290eeb6842fde946dd9bf817814c7178aaa

test/y4m_test.cc

@@ -141,11 +141,11 @@ class Y4mVideoWriteTest
   Y4mVideoWriteTest() {}
 
   virtual ~Y4mVideoWriteTest() {
-    CloseSource();
     delete tmpfile_;
+    input_file_ = NULL;
   }
 
-  virtual void ReplaceInputFile(FILE *input_file) {
+  void ReplaceInputFile(FILE *input_file) {
     CloseSource();
     frame_ = 0;
     input_file_ = input_file;