Moving connections to themselves crashes for PyQt5

[tj-jackman]

In 0.3.2 and onward, If I have a pair of connected nodes A->B, click-dragging the connection from B's input back onto B's input (i.e. the user choosing to leave a connection where it is) causes a crash in flow_scene.py:205 due to the UniqueConnection condition.

Example docker file which will crash running the example apps:

FROM debian:bullseye

RUN apt-get update --yes
RUN apt-get install --yes build-essential 
RUN apt-get install --yes make
RUN apt-get install --yes python3-dev
RUN apt-get install --yes python3
RUN apt-get install --yes python3-pip
RUN apt-get install --yes python3-setuptools
RUN apt-get install --yes python3-pyqt5
RUN apt-get install --yes python3-pyqt5.qtopengl
RUN apt-get install --yes mesa-utils
RUN apt-get install --yes libgl1-mesa-glx 
RUN apt-get install --yes libgl1-mesa-dri
RUN apt-get install --yes libglu1-mesa 
RUN apt-get install --yes xvfb
RUN apt-get install --yes git

RUN ln -s /usr/bin/python3 /usr/bin/python

RUN git clone https://github.com/klauer/qtpynodeeditor.git /tmp/qtpynodeeditor && \
    cd /tmp/qtpynodeeditor && \
    git checkout v0.3.2 && \
    python -m pip install .

RUN python -m pip install PyQt5
RUN python -m pip install pyqtgraph

ARG uid=1000
ARG gid=1000
RUN groupadd -g ${gid} user && \
    useradd -u ${uid} -g user -m user
USER user

WORKDIR /home/user/my_app

ENV PYTHONPATH="/home/user"
ENV LIBGL_ALWAYS_SOFTWARE=1
ENV QT_XCB_GL_INTEGRATION=none