IndexError from NOT OR foobar

[CodeOptimist]

A malformed query such as:

NOT OR foobar

throws IndexError: list index out of range in whoosh\qparser\syntax.py, line 376

class Wrapper(GroupNode):
    """Intermediate base class for nodes that wrap a single sub-node.
    """

    merging = False

    def query(self, parser):
        q = self.nodes[0].query(parser)  # <----- IndexError
        if q:
            return attach(self.qclass(q), self)

[<OP 'NOT'>, <OP 'OR'>, <None:'foobar'>] ➡️ [<NotGroup <OP 'OR'>>, <None:'foobar'>] ➡️ [<NotGroup >, <None:'foobar'>]

and <NotGroup > (no inner nodes) makes self.nodes[0] angry. 😄

Proposed fix:

    def query(self, parser):
        if self.nodes:  # <-----
            q = self.nodes[0].query(parser)
            if q:
                return attach(self.qclass(q), self)