OPENGLSDL: Make sure pipeline is destroyed when Manager is destroyed

When destroying the Manager its context is always destroyed.
Destroying OpenGLGraphicsManager must destroy the pipeline too.

backends/graphics/opengl/opengl-graphics.cpp

@@ -103,6 +103,7 @@ OpenGLGraphicsManager::~OpenGLGraphicsManager() {
 #if !USE_FORCED_GLES
 	ShaderManager::destroy();
 #endif
+	delete _pipeline;
 }
 
 bool OpenGLGraphicsManager::hasFeature(OSystem::Feature f) const {

backends/graphics/openglsdl/openglsdl-graphics.cpp

@@ -190,6 +190,10 @@ OpenGLSdlGraphicsManager::~OpenGLSdlGraphicsManager() {
 #if SDL_VERSION_ATLEAST(2, 0, 0)
 	notifyContextDestroy();
 	SDL_GL_DeleteContext(_glContext);
+#else
+	if (_hwScreen) {
+		notifyContextDestroy();
+	}
 #endif
 }