patch 8.1.0543: Coverity warns for leaking memory and using wrong struct

Problem:    Coverity warns for leaking memory and using wrong struct.
Solution:   Free pointer when allocation fails. Change "boff" to "loff".
            (closes #3634)
diff --git a/src/move.c b/src/move.c
index 214c362..a94a1ab 100644
--- a/src/move.c
+++ b/src/move.c
@@ -1961,7 +1961,7 @@
 	    scrolled += loff.height;
 	    if (loff.lnum == curwin->w_botline
 #ifdef FEAT_DIFF
-			    && boff.fill == 0
+			    && loff.fill == 0
 #endif
 		    )
 		scrolled -= curwin->w_empty_rows;