patch 8.1.1246: cannot handle negative mouse coordinate from urxvt

Problem:    Cannot handle negative mouse coordinate from urxvt.
Solution:   Accept '-' where a digit is expected. (Vincent Vinel,
            closes #4326)
diff --git a/src/version.c b/src/version.c
index 96f64eb..0e7f3f5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1246,
+/**/
     1245,
 /**/
     1244,