patch 8.1.2376: preprocessor indents are incorrect

Problem:    Preprocessor indents are incorrect.
Solution:   Fix the indents. (Ken Takata, closes #5298)
diff --git a/src/drawline.c b/src/drawline.c
index 95ade68..cb1c401 100644
--- a/src/drawline.c
+++ b/src/drawline.c
@@ -1940,11 +1940,11 @@
 		    c_final = NUL;
 		    if (VIM_ISWHITE(c))
 		    {
-#ifdef FEAT_CONCEAL
+# ifdef FEAT_CONCEAL
 			if (c == TAB)
 			    // See "Tab alignment" below.
 			    FIX_FOR_BOGUSCOLS;
-#endif
+# endif
 			if (!wp->w_p_list)
 			    c = ' ';
 		    }