Fixing build on gcc/clang

src/libslic3r/PNGReadWrite.cpp

@@ -149,6 +149,7 @@ static bool write_rgb_or_gray_to_file(const char *file_name_utf8, size_t width,
 
     // Initialize rows of PNG.
     row_pointers = reinterpret_cast<png_byte**>(::png_malloc(png_ptr, height * sizeof(png_byte*)));
+    {
         int line_width = width;
         if (png_color_type == PNG_COLOR_TYPE_RGB)
             line_width *= 3;
@@ -157,6 +158,7 @@ static bool write_rgb_or_gray_to_file(const char *file_name_utf8, size_t width,
             row_pointers[y] = row;
             memcpy(row, data + line_width * y, line_width);
         }
+    }
 
     // Write the image data to "fp".
     png_init_io(png_ptr, fp);