[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.
[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] Port to GStreamer 1.0