patch 9.0.0455: a few problems with 'splitscroll'

Problem:    A few problems with 'splitscroll'.
Solution:   Fix 'splitscroll' problems. (Luuk van Baal, closes #11117)
diff --git a/src/main.c b/src/main.c
index 2a2dcb0..619302a 100644
--- a/src/main.c
+++ b/src/main.c
@@ -375,7 +375,6 @@
      * Set the default values for the options that use Rows and Columns.
      */
     ui_get_shellsize();		// inits Rows and Columns
-    win_init_size();
 #ifdef FEAT_DIFF
     // Set the 'diff' option now, so that it can be checked for in a .vimrc
     // file.  There is no buffer yet though.
@@ -542,6 +541,7 @@
 	    mch_exit(1);
     }
 #endif
+    win_init_size();
 
 #ifdef FEAT_VIMINFO
     /*