vo_opengl: hwdec_cuda: fix crash when trying to use hwdec=cuda if cuda SDK is not present

If CUDA SDK wasn't installed, mpv crashed immediately with the message "Failed to load CUDA symbols"

video/out/opengl/hwdec_cuda.c

@@ -155,6 +155,7 @@ static int cuda_create(struct gl_hwdec *hw)
     bool loaded = cuda_load();
     if (!loaded) {
         MP_ERR(hw, "Failed to load CUDA symbols\n");
+        return -1;
     }
 
     ret = CHECK_CU(cuInit(0));