tl: fix detection of goto

Fixes #559.

* spot/tl/print.cc (strip_star_not): Only match a full star.
* tests/core/sugar.test: Add test case.

NEWS

@@ -219,6 +219,10 @@ New in spot 2.11.6.dev  (not yet released)
     fail to color some transiant edges when the "acd" option was
     activated.
 
+  - The formula printer incorrectly replaced a SERE like "(!a)[*3];a"
+    by "a[->]".  The latter should only replace "(!a)[*];a".
+    (Issue #559.)
+
 New in spot 2.11.6  (2023-08-01)
 
   Bug fixes:

spot/tl/print.cc

@@ -348,6 +348,8 @@ namespace spot
     static formula
     strip_star_not(formula f)
     {
+      if (!f.is_Kleene_star())
+        return nullptr;
       return f.get_child_of({op::Star, op::Not});
     }
 

tests/core/sugar.test

@@ -59,6 +59,10 @@ F[]a|G[]b|X[]c
 {##[1..2] b*}|->e
 {a ##[+] b}|->e
 {##[*] b}|->e
+{(!a)[*];a;b}!
+{(!a)[+];a;b}!
+{(!a)[*3];a;b}!
+{((!a)[*];a)[*2..3];b}!
 EOF
 
 ltlfilt -F ok.in > ok.out
@@ -99,6 +103,10 @@ FGa | Gb | XGc
 {[*1..2];b[*]}[]-> e
 {a;[*];b}[]-> e
 {[*];b}[]-> e
+{a[->];b}!
+{{!a}[+];a;b}!
+{{!a}[*3];a;b}!
+{a[->2..3];b}!
 EOF
 diff ok.out expect