display: Add NULL check for metadata

Add NULL pointer check for metatdata buffer before accessing its
member variable

Change-Id: I91de520b76d3c9714f357cff2de696e701811d06
CRs-Fixed: 434388
diff --git a/libhwcomposer/hwc_video.cpp b/libhwcomposer/hwc_video.cpp
index 1784593..16d0c89 100644
--- a/libhwcomposer/hwc_video.cpp
+++ b/libhwcomposer/hwc_video.cpp
@@ -108,7 +108,8 @@
     }
 
     MetaData_t *metadata = (MetaData_t *)hnd->base_metadata;
-    if ((metadata->operation & PP_PARAM_INTERLACED) && metadata->interlaced) {
+    if (metadata && (metadata->operation & PP_PARAM_INTERLACED) &&
+                                             metadata->interlaced) {
         ovutils::setMdpFlags(mdpFlags, ovutils::OV_MDP_DEINTERLACE);
     }