patch 8.0.0948: crash if timer closes window while dragging status line

Problem:    Crash if timer closes window while dragging status line.
Solution:   Check if the window still exists. (Yasuhiro Matsumoto, closes
            #1979)
diff --git a/src/version.c b/src/version.c
index ebfa0bf..b2de15d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    948,
+/**/
     947,
 /**/
     946,