Attempt to fix some crashes when adjusting material parameters

Sometimes I'm getting crashes when changing material parameters or when switching tabs in the object properties panel in Blender.

This is an old issue and I tried several changes, but still happens. I don't know if this is caused by some thread/concurrency problem or by deleting objects already deleted for some reason.

Just in case I'm doing some changes to try to avoid this. I hope they help and don't cause any other problems like memory leaks, etc.

src/bindings/yafrayinterface.i

@@ -175,6 +175,9 @@ public:
 
     virtual void initTilesPasses(int totalViews, int numExtPasses)
     { 
+		PyGILState_STATE gstate;
+		gstate = PyGILState_Ensure();
+
 		tilesPasses.resize(totalViews);
 
         for(size_t view = 0; view < tilesPasses.size(); ++view)
@@ -188,20 +191,27 @@ public:
 				tilesPasses.at(view)[idx]->resy = resy;
 			}
 		}
+
+		PyGILState_Release(gstate);
     }
 
 	virtual ~pyOutput_t()
 	{
+		PyGILState_STATE gstate;
+		gstate = PyGILState_Ensure();
+
 		for(size_t view = 0; view < tilesPasses.size(); ++view)
 		{
 			for(size_t idx = 0; idx < tilesPasses.at(view).size(); ++idx)
 			{
-				delete [] tilesPasses.at(view)[idx]->mem;
+				if(tilesPasses.at(view)[idx]->mem) delete [] tilesPasses.at(view)[idx]->mem;
 				//Py_XDECREF(tilesPasses.at(view)[idx]);
 			}
 			tilesPasses.at(view).clear();
 		}
 		tilesPasses.clear();
+
+		PyGILState_Release(gstate);
 	}
 
 	virtual bool putPixel(int numView, int x, int y, const yafaray::renderPasses_t *renderPasses, const std::vector<yafaray::colorA_t> &colExtPasses, bool alpha = true)