fixed wfs-connection triggering ssl-error response leading to crash

[notguiltyspark]

Description

When WFS connection fails during issuing connection request - opening/expanding connection-to-be-layer in the layer tree leads to the crash.

This is happening because the function,

QgsBaseNetworkRequest::issueRequest

that issues request, does not disconnect its local implementation from global singleton-emitted signals, leaving it hanging and reacting to it, when the local implementation/data is already gone (local mutex and waitCondition are destroyed on exiting function, but lambda-function, that uses them - resumeMainThread - reacts to the signal(s) through hanging connection(s) and tries to use them).

Thus explicit disconnects are provided to prevent this situation.

[github-actions]

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[rouault]

@notguiltyspark good catch! Would you mind applying the same type of change in src/core/network/qgsblockingnetworkrequest.cpp ? (yes, in an ideal world we wouldn't have that kind of duplicated code...)