bug fix mode_info_context not initialized for error-resilient

uninitialized xd->mode_info_context would crash
vpxenc for --error-resilient=1.

Change-Id: I31849e40281e3d65ab63257cfec5e93398997f0b

vp8/encoder/encodeframe.c

diff --git a/vp8/encoder/encodeframe.c b/vp8/encoder/encodeframe.c
index e694403..6a4995e 100644
--- a/vp8/encoder/encodeframe.c
+++ b/vp8/encoder/encodeframe.c
@@ -696,6 +696,8 @@
     cpi->last_mb_distortion = 0;
 #endif
 
+    xd->mode_info_context = cm->mi;
+
     vp8_zero(cpi->MVcount);
     vp8_zero(cpi->coef_counts);