patch 8.1.1207: some compilers give warning messages

Problem:    Some compilers give warning messages.
Solution:   Initialize variables, change printf() argument. (Christian
            Brabandt, closes #4305)
diff --git a/src/screen.c b/src/screen.c
index 67a0db9..862a635 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -549,8 +549,8 @@
 #endif
 #ifdef FEAT_GUI
     int		did_undraw = FALSE;
-    int		gui_cursor_col;
-    int		gui_cursor_row;
+    int		gui_cursor_col = 0;
+    int		gui_cursor_row = 0;
 #endif
     int		no_update = FALSE;