Fixed parsing of number of points for some shapes

The 18 and 28 need number of points, so we should read it.

Author: nijel

shapefile.py

@@ -336,7 +336,7 @@ def __shape(self):
         if shapeType in (3,5,13,15,23,25,31):
             nParts = unpack("<i", f.read(4))[0]
         # Shape types with points
-        if shapeType in (3,5,8,13,15,23,25,31):
+        if shapeType in (3,5,8,13,15,18,23,25,28,31):
             nPoints = unpack("<i", f.read(4))[0]
         # Read parts
         if nParts: