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/term.c b/src/term.c
index af7d27c..6fa519b 100644
--- a/src/term.c
+++ b/src/term.c
@@ -4551,10 +4551,11 @@
 			    continue;	/* no match */
 			else
 			{
-			    /* Skip over the digits, the final char must
-			     * follow. */
+			    // Skip over the digits, the final char must
+			    // follow. URXVT can use a negative value, thus
+			    // also accept '-'.
 			    for (j = slen - 2; j < len && (isdigit(tp[j])
-							 || tp[j] == ';'); ++j)
+				       || tp[j] == '-' || tp[j] == ';'); ++j)
 				;
 			    ++j;
 			    if (len < j)	/* got a partial sequence */
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,