Fix invalid assertion

BUG=aomedia:535

Change-Id: I514b2b0503e39023ae19b38a9b533bcd9abeee77

av1/decoder/decodeframe.c

diff --git a/av1/decoder/decodeframe.c b/av1/decoder/decodeframe.c
index 98d594f..5673fb8 100644
--- a/av1/decoder/decodeframe.c
+++ b/av1/decoder/decodeframe.c
@@ -4967,7 +4967,7 @@
 
 #if CONFIG_TEMPMV_SIGNALING
   if (cm->use_prev_frame_mvs) {
-    assert(!cm->error_resilient_mode && !cm->prev_frame &&
+    assert(!cm->error_resilient_mode && cm->prev_frame &&
            cm->width == last_fb_ref_buf->buf->y_width &&
            cm->height == last_fb_ref_buf->buf->y_height &&
            !cm->prev_frame->intra_only);