fix -Werror=misleading-indentation

fix -Werror=misleading-indentation

mines.c:551:9: error: this ‘for’ clause does not guard... [-Werror=misleading-indentation]
  551 |         for (int c = g.p[1]+plusminus; c >= 0 && c < f.w; c+=plusminus) \
      |         ^~~
mines.c:564:29: note: in expansion of macro ‘FIND_NEXT’
  564 |                             FIND_NEXT(CELL.o && CELL.n == what-'0', direction);
      |                             ^~~~~~~~~
mines.c:556:17: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘for’
  556 |                 return 0; \
      |                 ^~~~~~
mines.c:564:29: note: in expansion of macro ‘FIND_NEXT’
  564 |                             FIND_NEXT(CELL.o && CELL.n == what-'0', direction);
      |                             ^~~~~~~~~