Third set of checks of buffer level against maximum buffer size

Additional check of buffer level to ensure it doesn't exceed the
maximum buffer size.

Change-Id: I1ba4f8b09bbec89646885040ff47470196af521e

vp8/encoder/ratectrl.c

diff --git a/vp8/encoder/ratectrl.c b/vp8/encoder/ratectrl.c
index 1ac9050..dc6feb9 100644
--- a/vp8/encoder/ratectrl.c
+++ b/vp8/encoder/ratectrl.c
@@ -990,6 +990,8 @@
         {
             // Update the buffer level variable.
             cpi->bits_off_target += cpi->av_per_frame_bandwidth;
+            if (cpi->bits_off_target > cpi->oxcf.maximum_buffer_size)
+              cpi->bits_off_target = cpi->oxcf.maximum_buffer_size;
             cpi->buffer_level = cpi->bits_off_target;
         }
         else