Turned out that if you used explicit relative import syntax

(e.g. from .os import sep) and it failed, import would still try the implicit
relative import semantics of an absolute import (from os import sep). That's
not right, so when level is negative, only do explicit relative import
semantics.

Fixes issue #7902. Thanks to Meador Inge for the patch.

Python/import.c

@@ -2134,7 +2134,8 @@ import_module_level(char *name, PyObject *globals, PyObject *locals,
     if (parent == NULL)
         return NULL;
 
-    head = load_next(parent, Py_None, &name, buf, &buflen);
+    head = load_next(parent, level < 0 ? Py_None : parent, &name, buf,
+                        &buflen);
     if (head == NULL)
         return NULL;