Allow SkIcoCodec to fail due to conversion

src/codec/SkCodec_libico.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBmpCodec.h"
 #include "SkCodec_libico.h"
 #include "SkCodec_libpng.h"
@@ skipping 275 matching lines @@
                     kInvalidScale == result) {
                 SkCodecPrintf("Warning: Attempt to decode candidate ico failed.\n");
                 continue;
             }
 
             // On success or partial success, return the result
             return result;
         }
     }
 
-    // This should never be reached, since onDimensionsSupported should have rejected the
-    // dimensions sooner.
-    SkASSERT(false);
     SkCodecPrintf("Error: No matching candidate image in ico.\n");
     return result;
 }