bpo-38730: Replace strncpy in import.c with memcpy. (GH-17633)

In all these cases, we know the exact length we want copied, so memcpy is the right function to use.

Author: benjaminp

Python/import.c

@@ -2456,7 +2456,7 @@ get_parent(PyObject *globals, char *buf, Py_ssize_t *p_buflen, int level)
 "Module name too long");
 returnNULL;
  }
-strncpy(buf, start, len);
+memcpy(buf, start, len);
 buf[len] ='\0';
 pkgname=PyString_FromString(buf);
 if (pkgname==NULL) {
@@ -2554,7 +2554,7 @@ load_next(PyObject *mod, PyObject *altmod, char **p_name, char *buf,
 "Module name too long");
 returnNULL;
  }
-strncpy(p, name, len);
+memcpy(p, name, len);
 p[len] ='\0';
 *p_buflen=p+len-buf;
 
@@ -2568,7 +2568,7 @@ load_next(PyObject *mod, PyObject *altmod, char **p_name, char *buf,
 Py_DECREF(result);
 returnNULL;
  }
-strncpy(buf, name, len);
+memcpy(buf, name, len);
 buf[len] ='\0';
 *p_buflen=len;
  }