Return zero from ImagePath compact() if there are no points to remove

Tests/test_imagepath.py

@@ -216,6 +216,11 @@ def test_overflow_segfault() -> None:
             x[i] = b"0" * 16
 
 
+def test_compact_empty_path() -> None:
+    p = ImagePath.Path(0)
+    assert p.compact() == 0
+
+
 def test_compact_within_map() -> None:
     p = ImagePath.Path([0, 1])
 

src/path.c

@@ -326,6 +326,10 @@ path_compact(PyPathObject *self, PyObject *args) {
         PyErr_SetString(PyExc_ValueError, "Path compacted during mapping");
         return NULL;
     }
+    if (self->count == 0) {
+        // no points to remove
+        return Py_BuildValue("i", 0);
+    }
     if (!PyArg_ParseTuple(args, "|d:compact", &cityblock)) {
         return NULL;
     }