Improper error message

Describe the bug
Try to execute an empty string should not complain about multiple queries

To Reproduce

conn = monetdbe.connect(':memory:')
res = conn.execute("""""")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/ufs/mk/.virtualenvs/python-Kt-6h5O5/lib/python3.7/site-packages/monetdbe/connection.py", line 100, in execute
    cur = Cursor(con=self).execute(query, args)
  File "/ufs/mk/.virtualenvs/python-Kt-6h5O5/lib/python3.7/site-packages/monetdbe/cursor.py", line 142, in execute
    raise Warning("Multiple queries in one execute() call")
monetdbe.exceptions.Warning: Multiple queries in one execute() call

Expected behavior
Either considered as a no-op or a proper error message

Software versions

• OS and version: OSX
  Python version: 3.7.7
• MonetDBe-Python version: 0.7.1

Additional context
Add any other context about the problem here.

[gijzelaerr]

This issue has been resolved.