patch 8.0.1374: CTRL-A does not work with an empty line

Problem:    CTRL-A does not work with an empty line. (Alex)
Solution:   Decrement the end only once. (Hirohito Higashi, closes #2387)
diff --git a/src/ops.c b/src/ops.c
index e366903..0209334 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -5433,7 +5433,7 @@
 	    }
 	    else /* oap->motion_type == MCHAR */
 	    {
-		if (!oap->inclusive)
+		if (pos.lnum == oap->start.lnum && !oap->inclusive)
 		    dec(&(oap->end));
 		length = (colnr_T)STRLEN(ml_get(pos.lnum));
 		pos.col = 0;