Renderer GL: Don't leak shader/UBO handles

include/renderer_gl/renderer_gl.hpp

@@ -117,6 +117,7 @@ class RendererGL final : public Renderer {
 	// Note: The caller is responsible for deleting the currently bound FBO before calling this
 	void setFBO(uint handle) { screenFramebuffer.m_handle = handle; }
 	void resetStateManager() { gl.reset(); }
+	void clearShaderCache();
 	void initUbershader(OpenGL::Program& program);
 
 #ifdef PANDA3DS_FRONTEND_QT