[libpng16] zero out memory allocated by png_inflate

pngrutil.c

@@ -670,6 +670,10 @@ png_decompress_chunk(png_structrp png_ptr,
                    (terminate != 0);
                png_bytep text = png_voidcast(png_bytep, png_malloc_base(png_ptr,
                    buffer_size));
+               /* attempt to stop an oss-fuzz "use of uninitialized value"
+                * in png_set_text_2()
+                */
+               memset(text, 0, buffer_size);
 
                if (text != NULL)
                {