fixup! Search sys.path for PEP-561 compliant packages

Author: AWhetter

mypy/modulefinder.py

@@ -247,6 +247,8 @@ def _find_module_non_stub_helper(self, components: List[str],
             elif not plausible_match and (self.fscache.isdir(dir_path)
                                           or self.fscache.isfile(dir_path + ".py")):
                 plausible_match = True
+            if not self.fscache.isdir(dir_path):
+                break
         if is_legacy_bundled_package(components[0], self.python_major_ver):
             if (len(components) == 1
                     or (self.find_module(components[0]) is