patches/ExternalMethod update patch for Zope4

In the changes from ExternalMethod 2.13.1 -> 4.5, now ExternalMethod
define __code__ (and __defaults__) to a computed attribute calling
getFunction, but getFunction is different in our patched class, so
when unwrapMethod tries to get __code__, it will raise and mapply
will not consider the external method as being callable, so a simple
__repr__ of the ExternalMethod will be used as response body when
published.

By defining __code__ to something using our patched logic, this
problem does not happen.

There's also a TODO because DevelopmentMode is now True, which uses
a different code path which was causing TypeError, because getPath
returns None, which os.stat does not accept.

product/ERP5Type/patches/ExternalMethod.py

@@ -61,6 +61,7 @@ class _(PatchClass(ExternalMethod)):
         if component_module is None:
             # Fall back on filesystem
             if not reload:
+                # TODO Zope4: DevelopmentMode is True ( on Zope2 Globals.DevelopmentMode was False )
                 from Products.ERP5Type.Globals import DevelopmentMode
                 if DevelopmentMode:
                     try:
@@ -69,10 +70,11 @@ class _(PatchClass(ExternalMethod)):
                         last_read = None
                         path = getPath('Extensions', self._module,
                                        suffixes=('', 'py', 'pyc'))
-                    ts = os.stat(path)[stat.ST_MTIME]
-                    if last_read != ts:
-                        self._v_fs = ts, path
-                        reload = True
+                    if path:
+                        ts = os.stat(path)[stat.ST_MTIME]
+                        if last_read != ts:
+                            self._v_fs = ts, path
+                            reload = True
             f = getObject(self._module, self._function, reload)
         else:
             f = getattr(component_module, self._function)