avcodec/nvenc: fix segfault in intra-only mode

In intra-only mode, frameIntervalP is 0, which means the frame
data array is smaller than the number of surfaces.

Together with using the wrong size on deallocation of the
frame_data_array, this lead to a crash.

Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>
(cherry picked from commit c9151ea507)

libavcodec/nvenc.c

@@ -982,7 +982,7 @@ static av_cold int nvenc_recalc_surfaces(AVCodecContext *avctx)
 
     // Output in the worst case will only start when the surface buffer is completely full.
     // Hence we need to keep at least the max amount of surfaces plus the max reorder delay around.
-    ctx->frame_data_array_nb = ctx->nb_surfaces + ctx->encode_config.frameIntervalP - 1;
+    ctx->frame_data_array_nb = FFMAX(ctx->nb_surfaces, ctx->nb_surfaces + ctx->encode_config.frameIntervalP - 1);
 
     return 0;
 }
@@ -1891,7 +1891,7 @@ av_cold int ff_nvenc_encode_close(AVCodecContext *avctx)
     av_fifo_freep2(&ctx->unused_surface_queue);
 
     if (ctx->frame_data_array) {
-        for (i = 0; i < ctx->nb_surfaces; i++)
+        for (i = 0; i < ctx->frame_data_array_nb; i++)
             av_buffer_unref(&ctx->frame_data_array[i].frame_opaque_ref);
         av_freep(&ctx->frame_data_array);
     }