GEOSConcaveHullOfPolygons: Avoid crash on zero-area input (#1076)

* GEOSConcaveHullOfPolygons: Avoid crash on zero-area input

Resolves #1071

Author: dbaston

src/algorithm/hull/ConcaveHullOfPolygons.cpp

@@ -156,7 +156,7 @@ ConcaveHullOfPolygons::setTight(bool p_isTight)
 std::unique_ptr<Geometry>
 ConcaveHullOfPolygons::getHull()
 {
-    if (inputPolygons->isEmpty()) {
+    if (inputPolygons->isEmpty() || inputPolygons->getArea() == 0) {
         return createEmptyHull();
     }
     buildHullTris();

tests/unit/capi/GEOSConcaveHullOfPolygonsTest.cpp

@@ -62,6 +62,15 @@ void object::test<3>()
     result_ = GEOSConcaveHullOfPolygons(input_, 0.7, false, false);
     ensure("curved geometry not supported", result_ == nullptr);
 }
+  
+template<>
+template<>
+void object::test<4>()
+{
+    input_ = fromWKT("POLYGON((0 0, 0 0, 0 0))");
+    result_ = GEOSConcaveHullOfPolygons(input_, 0.7, false, false);
+    ensure(GEOSisEmpty(result_));
+}
 
 
 } // namespace tut