Fix reverse multilink iteration

Adding a reverse multilink to *the same class* would trigger a traceback
about a modified dictionary on iteration

Author: schlatterbeck

CHANGES.txt

@@ -11,6 +11,12 @@ Python v2.5 and v2.6.  Starting with the v1.6 releases of Roundup
 v2.7.2 or later are required to run newer releases of Roundup.  From v2.0
 onwards Python 3.4 and later are also supported.
 
+XXXX-XX-XX 2.0.1
+
+Fixed:
+- Reverse multilink to *the same class* would trigger a traceback about
+  a modified dictionary on iteration (Ralf Schlatterbeck)
+
 2020-07-13 2.0.0
 
 Fixed:

roundup/hyperdb.py

@@ -875,7 +875,9 @@ def post_init(self):
         done = getattr(self, 'post_init_done', None)
         for cn in self.getclasses():
             cl = self.getclass(cn)
-            for p in cl.properties:
+            # This will change properties if a back-multilink happens to
+            # have the same class, so we need to iterate over .keys()
+            for p in cl.properties.keys():
                 prop = cl.properties[p]
                 if not isinstance (prop, (Link, Multilink)):
                     continue