Do not create empty color table if it does not exist

src/codec/SkCodec_libbmp.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 "SkCodec_libbmp.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
@@ skipping 552 matching lines @@
         return false;
     }
 
     // After reading the color table, skip to the start of the pixel array
     if (stream()->skip(fOffset - colorBytes) != fOffset - colorBytes) {
         SkDebugf("Error: unable to skip to image data.\n");
         return false;
     }
 
     // Set the color table and return true on success
-    fColorTable.reset(SkNEW_ARGS(SkColorTable, (colorTable, maxColors)));
+    if (maxColors > 0) {
+        fColorTable.reset(SkNEW_ARGS(SkColorTable, (colorTable, maxColors)));
+    }
     return true;
 }
 
 /*
  *
  * Performs the bitmap decoding for bit masks input format
  *
  */
 SkCodec::Result SkBmpCodec::decodeMask(const SkImageInfo& dstInfo,
                                        void* dst, size_t dstRowBytes) {
@@ skipping 416 matching lines @@
                 }
                 dstRow = SkTAddOffset<SkPMColor>(dstRow, dstRowBytes);
             }
         }
     }
     */
 
     // Finished decoding the entire image
     return kSuccess;
 }