Bugfix: prevent fatal error in the rare case that no bridge anchors are found. #1607

lib/Slic3r/Layer/Region.pm

@@ -484,6 +484,7 @@ sub _detect_bridge_direction {
             1,  # safety offset required to avoid Clipper from detecting empty intersection while Boost actually found some @edges
         );
         
+        if (@$anchors) {
             # we'll now try several directions using a rudimentary visibility check:
             # bridge in several directions and then sum the length of lines having both
             # endpoints within anchors
@@ -523,6 +524,7 @@ sub _detect_bridge_direction {
             # the best direction is the one causing most lines to be bridged
             $bridge_angle = Slic3r::Geometry::rad2deg_dir($sorted_directions[-1]);
         }
+    }
     
     Slic3r::debugf "  Optimal infill angle of bridge on layer %d is %d degrees\n",
         $self->id, $bridge_angle if defined $bridge_angle;