patch 8.0.0425: build errors when building without folding

Problem:    Build errors when building without folding.
Solution:   Add #ifdefs. (John Marriott)
diff --git a/src/option.c b/src/option.c
index d4e760b..b0baf50 100644
--- a/src/option.c
+++ b/src/option.c
@@ -4535,8 +4535,11 @@
 		 * "wrap" gets set. */
 		if (curwin->w_p_diff
 			&& opt_idx >= 0  /* shut up coverity warning */
-			&& (options[opt_idx].indir == PV_FDM
-			    || options[opt_idx].indir == PV_WRAP))
+			&& (
+#ifdef FEAT_FOLDING
+			    options[opt_idx].indir == PV_FDM ||
+#endif
+			    options[opt_idx].indir == PV_WRAP))
 		    goto skip;
 #endif
 	    }