Clamp current_delta_lf_from_base in ext_delta_q

BUG=aomedia:829

Change-Id: I78347e12b4efa05ebd424ba25de7767437495b42

av1/decoder/decodemv.c

@@ -1142,10 +1142,12 @@ static void read_intra_frame_mode_info(AV1_COMMON *const cm,
         xd->prev_delta_lf_from_base = xd->current_delta_lf_from_base;
       }
 #else
-      mbmi->current_delta_lf_from_base = xd->current_delta_lf_from_base =
+      const int current_delta_lf_from_base =
           xd->prev_delta_lf_from_base +
           read_delta_lflevel(cm, xd, r, mbmi, mi_col, mi_row) *
               cm->delta_lf_res;
+      mbmi->current_delta_lf_from_base = xd->current_delta_lf_from_base =
+          clamp(current_delta_lf_from_base, 0, MAX_LOOP_FILTER);
       xd->prev_delta_lf_from_base = xd->current_delta_lf_from_base;
 #endif  // CONFIG_LOOPFILTER_LEVEL
     }
@@ -2897,10 +2899,12 @@ static void read_inter_frame_mode_info(AV1Decoder *const pbi,
         xd->prev_delta_lf_from_base = xd->current_delta_lf_from_base;
       }
 #else
-      mbmi->current_delta_lf_from_base = xd->current_delta_lf_from_base =
+      const int current_delta_lf_from_base =
           xd->prev_delta_lf_from_base +
           read_delta_lflevel(cm, xd, r, mbmi, mi_col, mi_row) *
               cm->delta_lf_res;
+      mbmi->current_delta_lf_from_base = xd->current_delta_lf_from_base =
+          clamp(current_delta_lf_from_base, 0, MAX_LOOP_FILTER);
       xd->prev_delta_lf_from_base = xd->current_delta_lf_from_base;
 #endif  // CONFIG_LOOPFILTER_LEVEL
     }

av1/encoder/encodeframe.c

@@ -4730,7 +4730,8 @@ static void encode_rd_sb_row(AV1_COMP *cpi, ThreadData *td,
         for (j = 0; j < AOMMIN(cm->mib_size, cm->mi_rows - mi_row); j++) {
           for (k = 0; k < AOMMIN(cm->mib_size, cm->mi_cols - mi_col); k++) {
             cm->mi[(mi_row + j) * cm->mi_stride + (mi_col + k)]
-                .mbmi.current_delta_lf_from_base = current_delta_lf_from_base;
+                .mbmi.current_delta_lf_from_base =
+                clamp(current_delta_lf_from_base, 0, MAX_LOOP_FILTER);
 #if CONFIG_LOOPFILTER_LEVEL
             for (int lf_id = 0; lf_id < FRAME_LF_COUNT; ++lf_id) {
               cm->mi[(mi_row + j) * cm->mi_stride + (mi_col + k)]