Avoid errors when metadata directory is broken. Ref #419.

CHANGES.txt

@@ -9,6 +9,8 @@ CHANGES
 
 * Issue #471: Don't rely on repr for an HTML attribute value in
   package_index.
+* Issue #419: Avoid errors in FileMetadata when the metadata directory
+  is broken.
 
 ------
 18.7.1

pkg_resources/__init__.py

@@ -2017,7 +2017,7 @@ class FileMetadata(EmptyProvider):
         self.path = path
 
     def has_metadata(self, name):
-        return name=='PKG-INFO'
+        return name=='PKG-INFO' and os.path.isfile(self.path)
 
     def get_metadata(self, name):
         if name=='PKG-INFO':