Fix and test for LargestEmptyCircle crash on malformed input (#1004)

* Fix and tests for GH-1003
* Call to init() was missing? Does not explain why the bug in the original issue seemed tied to particular coordinates, as the fix will apply across all inputs. So be warned, there may still be something hiding in there.

src/algorithm/construct/IndexedDistanceToPoint.cpp

@@ -36,7 +36,7 @@ IndexedDistanceToPoint::IndexedDistanceToPoint(const Geometry& geom)
 void IndexedDistanceToPoint::init()
 {
     if (facetDistance != nullptr)
-      return;
+        return;
     ptLocator.reset(new IndexedPointInPolygonsLocator(targetGeometry));
     facetDistance.reset(new IndexedFacetDistance(&targetGeometry));
 }
@@ -62,7 +62,8 @@ bool IndexedDistanceToPoint::isInArea(const Point& pt)
 std::unique_ptr<geom::CoordinateSequence> 
 IndexedDistanceToPoint::nearestPoints(const Point& pt)
 {
+    init();
     return facetDistance->nearestPoints(&pt);
 }
 
-}}}
+}}}

tests/unit/algorithm/construct/LargestEmptyCircleTest.cpp

@@ -316,4 +316,30 @@ void object::test<19>()
         0.01, 5.5, 4.5, 2.12 );
 }
 
+
+// https://trac.osgeo.org/postgis/ticket/5626
+template<>
+template<>
+void object::test<20>()
+{
+    checkCircle(
+        "POINT(-11 40)", // input
+        "POLYGON((-71.1 42.3,-71.1 42.4,-71.2 42.3,-71.1 42.3))", // boundary
+        0.1, // test tolerance
+        -71.15, 42.34, 60.19588 ); // expected x, y, radius
+}
+
+
+// https://trac.osgeo.org/postgis/ticket/5626
+template<>
+template<>
+void object::test<21>()
+{
+    checkCircle(
+        "POINT(-11.1111111 40)", // input
+        "POLYGON((-71.0821 42.3036,-71.0821 42.3936,-71.0901 42.3036,-71.0821 42.3036))", // boundary
+        1, // test tolerance
+        -71.15, 42.34, 60.19588 ); // expected x, y, radius
+}
+
 } // namespace tut