[Bitmap] Add null pointer protection in Bitmap_sameAs()

    const int h = bm0->height();

    const size_t size = bm0->width() * bm0->bytesPerPixel();

    for (int y = 0; y < h; y++) {

        if (memcmp(bm0->getAddr(0, y), bm1->getAddr(0, y), size) != 0) {

        // SkBitmap::getAddr(int, int) may return NULL due to unrecognized config

        // (ex: kRLE_Index8_Config). This will cause memcmp method to crash. Since bm0

        // and bm1 both have pixel data() (have passed NULL == getPixels() check),

        // those 2 bitmaps should be valid (only unrecognized), we return JNI_FALSE

        // to warn user those 2 unrecognized config bitmaps may be different.

        void *bm0Addr = bm0->getAddr(0, y);

        void *bm1Addr = bm1->getAddr(0, y);

        if(bm0Addr == NULL || bm1Addr == NULL) {

            return JNI_FALSE;

        }

        if (memcmp(bm0Addr, bm1Addr, size) != 0) {

            return JNI_FALSE;

        }

    }