Check fopen failure in print_reconstruction_frame

Fix Coverity defect CID 561345 Dereference null return value.

Change-Id: I0b7f37c6adc6b9ec478404a3e1a45224fee4a397

av1/encoder/firstpass.c

diff --git a/av1/encoder/firstpass.c b/av1/encoder/firstpass.c
index 30d3522..bbd5b2d 100644
--- a/av1/encoder/firstpass.c
+++ b/av1/encoder/firstpass.c
@@ -12,6 +12,7 @@
 #include <limits.h>
 #include <math.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 #include "config/aom_dsp_rtcd.h"
 #include "config/aom_scale_rtcd.h"
@@ -1046,6 +1047,11 @@
     recon_file = fopen(filename, "ab");
   }
 
+  if (!recon_file) {
+    fprintf(stderr, "%s: fopen(\"%s\") failed", __func__, filename);
+    abort();
+  }
+
   fwrite(last_frame->buffer_alloc, last_frame->frame_size, 1, recon_file);
   fclose(recon_file);
 }