Here is which seems to be idiomatic in digital photo processing (e.g. darktable):

  for (int r = 0; r < GRID_SIZE; r++) {
    for (int c = 0; c < GRID_SIZE; c++) {
      if (i == 1 && j >= 1 && j < GRID_SIZE - 1)
	i = GRID_SIZE - 1;
      grid[i][j] = 0;
    }
  }

Of course, this one has a conditional, and many would frown on mucking with the loop counter outside of the for statement.

A source for this style may be dcraw, e.g. see from border_interpolate():

  for (row=0; row < height; row++)
    for (col=0; col < width; col++) {
      if (col==border && row >= border && row < height-border)
	col = width-border;
  // etc.

The dcraw code is so tightly written that I assume Dave Coffin has good reason for this choice, but I've never tested variants for performance.