[nemo-qtmultimedia-plugins] Fix crash on destruction during playback.

Disconnect the signal handler on destruction so it isn't invoked
later on.
Merge pull request #1 from adenexter/destruction-crash

[nemo-qtmultimedia-plugins] Fix crash on destruction during playback.
[nemo-qtmultimedia-plugins] Fix initialization of properties.

Query the values of mirror and orientation on initialization instead
of waiting for a change notifier that may never come.
[nemo-qtmultimedia-plugins] Don't change state during rendering.

This is not a problem today, but changing the state during rendering
is not supported in the scene graph and because the texture change
does not flag the scene graph with a dirty material we might run
into this issue as a missing repaint down the line.
Merge pull request #2 from adenexter/init

[nemo-qtmultimedia-plugins] Fix initialization of properties.
[nemo-qtmultimedia-plugins] Fix crash if plugin is destroyed in the frame handler.
Merge pull request #4 from adenexter/frame-ready-crash

[nemo-qtmultimedia-plugins] Fix crash if plugin is destroyed in the fram...
Merge pull request #3 from sletta/no-change-during-rendering

[nemo-qtmultimedia-plugins] Don't change state during rendering.
[nemo-qtmultimedia-plugins] Ensure new nodes have valid geometry.

Set the geometryChanged flag after creating a new node otherwise its
geometry won't be initialized unless something else coincidentally set
the flag.