{decodeframe,rdopt}.c: fix asserts with strings

lead with '0 &&' to avoid string to bool conversion warnings

BUG=aomedia:621

Change-Id: I2cd6618377f9ed94f4d9dbc252f6f5cfc81efea4

av1/decoder/decodeframe.c

@@ -3393,7 +3393,7 @@ static int mem_get_varsize(const uint8_t *src, int sz) {
     case 2: return mem_get_le16(src);
     case 3: return mem_get_le24(src);
     case 4: return mem_get_le32(src);
-    default: assert("Invalid size" && 0); return -1;
+    default: assert(0 && "Invalid size"); return -1;
   }
 }
 

av1/encoder/rdopt.c

@@ -6056,7 +6056,7 @@ static void single_motion_search(const AV1_COMP *const cpi, MACROBLOCK *x,
           MAX_MVSEARCH_STEPS - 1 - step_param, 1, &cpi->fn_ptr[bsize], &ref_mv,
           &(x->best_mv.as_mv), 0);
       break;
-    default: assert("Invalid motion mode!\n");
+    default: assert(0 && "Invalid motion mode!\n");
   }
 #endif  // CONFIG_MOTION_VAR
 
@@ -6136,7 +6136,7 @@ static void single_motion_search(const AV1_COMP *const cpi, MACROBLOCK *x,
             cpi->sf.mv.subpel_iters_per_step, x->nmvjointcost, x->mvcost, &dis,
             &x->pred_sse[ref], 0, cpi->sf.use_upsampled_references);
         break;
-      default: assert("Invalid motion mode!\n");
+      default: assert(0 && "Invalid motion mode!\n");
     }
 #endif  // CONFIG_MOTION_VAR
   }