Fixed crashes with specific configuration of draft shield:

the crashing cases were:
- skirts=0 + dsEnabled
- skirt_height=0 + dsLimited

Also, when ooze_prevention is enabled with multiple extruders and skirt is disabled, 2.4.0 does not generate infinite skirt.
Version 2.3.3 does, ooze prevention overrides the disabled skirt. This commit reinstates the old behaviour.

The issues were introduced in b466f18.

src/libslic3r/Print.cpp

@@ -349,7 +349,9 @@ bool Print::has_infinite_skirt() const
 
 bool Print::has_skirt() const
 {
-    return (m_config.skirt_height > 0 && m_config.skirts > 0) || m_config.draft_shield != dsDisabled;
+    return (m_config.skirt_height > 0 && m_config.skirts > 0) || has_infinite_skirt();
+    // case dsLimited should only be taken into account when skirt_height and skirts are positive,
+    // so it is covered by the first condition.
 }
 
 bool Print::has_brim() const