error check vp9 superframe parsing

This patch insures that the last byte of a chunk that contains a
valid superframe marker byte,  actually has a proper superframe index.
If not it returns an error.

As part of doing that the file : vp90-2-15-fuzz-flicker.webm now fails
to decode properly and moves to the invalid file test from the test
vector suite.

Change-Id: I5f1da7eb37282ec0c6394df5c73251a2df9c1744

test/invalid_file_test.cc

@@ -94,7 +94,8 @@ TEST_P(InvalidFileTest, ReturnCode) {
 }
 
 const char *const kVP9InvalidFileTests[] = {
-  "invalid-vp90-01.webm"
+  "invalid-vp90-01.webm",
+  "invalid-vp90-02.webm"
 };
 
 #define NELEMENTS(x) static_cast<int>(sizeof(x) / sizeof(x[0]))