Fix NPDs in h263 decoder

Bug: 35269635
Test: decoded PoC with and without patch
Change-Id: I636a14360c7801cc5bca63c9cb44d1d235df8fd8
(cherry picked from commit 2ad2a92318a3b9daf78ebcdc597085adbf32600d)
diff --git a/media/libstagefright/codecs/m4v_h263/dec/src/mb_motion_comp.cpp b/media/libstagefright/codecs/m4v_h263/dec/src/mb_motion_comp.cpp
index fbc7be1..877723d 100644
--- a/media/libstagefright/codecs/m4v_h263/dec/src/mb_motion_comp.cpp
+++ b/media/libstagefright/codecs/m4v_h263/dec/src/mb_motion_comp.cpp
@@ -15,6 +15,10 @@
  * and limitations under the License.
  * -------------------------------------------------------------------
  */
+
+#define LOG_TAG "m4v_h263"
+#include <log/log.h>
+
 /*
 ------------------------------------------------------------------------------
  INPUT AND OUTPUT DEFINITIONS
@@ -236,6 +240,11 @@
 
     /* Pointer to previous luminance frame */
     c_prev  = prev->yChan;
+    if (!c_prev) {
+        ALOGE("b/35269635");
+        android_errorWriteLog(0x534e4554, "35269635");
+        return;
+    }
 
     pred_block = video->mblock->pred_block;
 
@@ -574,7 +583,14 @@
 
     /* zero motion compensation for previous frame */
     /*mby*width + mbx;*/
-    c_prev  = prev->yChan + offset;
+    c_prev  = prev->yChan;
+    if (!c_prev) {
+        ALOGE("b/35269635");
+        android_errorWriteLog(0x534e4554, "35269635");
+        return;
+    }
+    c_prev += offset;
+
     /*by*width_uv + bx;*/
     cu_prev = prev->uChan + (offset >> 2) + (xpos >> 2);
     /*by*width_uv + bx;*/
diff --git a/media/libstagefright/codecs/m4v_h263/dec/src/pvdec_api.cpp b/media/libstagefright/codecs/m4v_h263/dec/src/pvdec_api.cpp
index c1720c6..8d5d071 100644
--- a/media/libstagefright/codecs/m4v_h263/dec/src/pvdec_api.cpp
+++ b/media/libstagefright/codecs/m4v_h263/dec/src/pvdec_api.cpp
@@ -15,6 +15,8 @@
  * and limitations under the License.
  * -------------------------------------------------------------------
  */
+#define LOG_TAG "pvdec_api"
+#include <log/log.h>
 #include "mp4dec_lib.h"
 #include "vlc_decode.h"
 #include "bitstream.h"
@@ -1335,6 +1337,11 @@
             }
         }
 
+        if (!video->prevVop->yChan) {
+            ALOGE("b/35269635");
+            android_errorWriteLog(0x534e4554, "35269635");
+            return PV_FALSE;
+        }
         oscl_memcpy(currVop->yChan, video->prevVop->yChan, (decCtrl->size*3) / 2);
 
         video->prevVop = prevVop;