vpxdec: report parse errors from webm_guess_framerate()

If this function fails silently, the nestegg context is destroyed and
future nestegg calls will segfault.

Change-Id: Ie6a0ea284ab9ddfa97b1843ef8030a953937c8cd

vpxdec.c

diff --git a/vpxdec.c b/vpxdec.c
index 85ab206..9b565b0 100644
--- a/vpxdec.c
+++ b/vpxdec.c
@@ -542,6 +542,7 @@
     *fps_den = tstamp / 1000;
     return 0;
 fail:
+    nestegg_destroy(input->nestegg_ctx);
     input->nestegg_ctx = NULL;
     rewind(input->infile);
     return 1;
@@ -878,7 +879,13 @@
         }
 
         if(input.kind == WEBM_FILE)
-            webm_guess_framerate(&input, &fps_den, &fps_num);
+            if(webm_guess_framerate(&input, &fps_den, &fps_num))
+            {
+                fprintf(stderr, "Failed to guess framerate -- error parsing "
+                                "webm file?\n");
+                return EXIT_FAILURE;
+            }
+
 
         /*Note: We can't output an aspect ratio here because IVF doesn't
            store one, and neither does VP8.