lpe-knot: fix crash

diff --git a/src/live_effects/lpe-knot.cpp b/src/live_effects/lpe-knot.cpp
index b3aa2df459e1961a975b9a168ffed6ddcbe54775..b8e9b8cf9609bd6d858d9eea25a579a6d6c92e22 100644 (file)
--- a/src/live_effects/lpe-knot.cpp
+++ b/src/live_effects/lpe-knot.cpp
@@ -56,17 +56,19 @@ public:
 static
 std::vector<Geom::Interval> complementOf(Geom::Interval I, std::vector<Geom::Interval> domain){
     std::vector<Geom::Interval> ret;
-    double min = domain.front().min();
-    double max = domain.back().max();
-    Geom::Interval I1 = Geom::Interval(min,I.min());
-    Geom::Interval I2 = Geom::Interval(I.max(),max);
-
-    for (unsigned i = 0; i<domain.size(); i++){
-        boost::optional<Geom::Interval> I1i = intersect(domain.at(i),I1);
-        if (I1i && !I1i->isSingular()) ret.push_back(I1i.get());
-        boost::optional<Geom::Interval> I2i = intersect(domain.at(i),I2);
-        if (I2i && !I2i->isSingular()) ret.push_back(I2i.get());
-    }    
+    if (!domain.empty()) {
+        double min = domain.front().min();
+        double max = domain.back().max();
+        Geom::Interval I1 = Geom::Interval(min,I.min());
+        Geom::Interval I2 = Geom::Interval(I.max(),max);
+
+        for (unsigned i = 0; i<domain.size(); i++){
+            boost::optional<Geom::Interval> I1i = intersect(domain.at(i),I1);
+            if (I1i && !I1i->isSingular()) ret.push_back(I1i.get());
+            boost::optional<Geom::Interval> I2i = intersect(domain.at(i),I2);
+            if (I2i && !I2i->isSingular()) ret.push_back(I2i.get());
+        }
+    }
     return ret;
 }