Use a local vstat copy instead of cvstat to avoid holding the lock

for an extended time.  Should fix SDL mode slowness.

Only call RenderPresent() if we called RenderCopy().  Should fix
SDL mode flickering.

src/conio/sdl_con.c

@@ -1060,6 +1060,8 @@ void sdl_video_event_thread(void *data)
 						return;
 					case SDL_USEREVENT_FLUSH:
 						pthread_mutex_lock(&vstatlock);
+						struct video_stats lvstat = cvstat;
+						pthread_mutex_unlock(&vstatlock);
 						pthread_mutex_lock(&win_mutex);
 						if (win != NULL) {
 							pthread_mutex_lock(&sdl_headlock);
@@ -1080,19 +1082,19 @@ void sdl_video_event_thread(void *data)
 									int row;
 									int tw, th;
 
-									sdl.RenderClear(renderer);
 									if (internal_scaling) {
 										struct graphics_buffer *gb;
 										int xscale, yscale;
-										internal_scaling_factors(cvstat.winwidth, cvstat.winheight, &xscale, &yscale);
+										internal_scaling_factors(lvstat.winwidth, lvstat.winheight, &xscale, &yscale);
 										gb = do_scale(list, xscale, yscale,
-										    cvstat.aspect_width, cvstat.aspect_height);
+										    lvstat.aspect_width, lvstat.aspect_height);
 										src.x = 0;
 										src.y = 0;
 										src.w = gb->w;
 										src.h = gb->h;
 										if (sdl.QueryTexture(texture, NULL, NULL, &tw, &th) != 0)
 											fprintf(stderr, "Unable to query texture (%s)\n", sdl.GetError());
+										sdl.RenderClear(renderer);
 										if (sdl.LockTexture(texture, &src, &pixels, &pitch) != 0)
 											fprintf(stderr, "Unable to lock texture (%s)\n", sdl.GetError());
 										if (pitch != gb->w * sizeof(gb->data[0])) {
@@ -1112,8 +1114,8 @@ void sdl_video_event_thread(void *data)
 											memcpy(pixels, gb->data, gb->w * ch * sizeof(gb->data[0]));
 										}
 										sdl.UnlockTexture(texture);
-										dst.x = (cvstat.winwidth - gb->w) / 2;
-										dst.y = (cvstat.winheight - gb->h) / 2;
+										dst.x = (lvstat.winwidth - gb->w) / 2;
+										dst.y = (lvstat.winheight - gb->h) / 2;
 										dst.w = gb->w;
 										dst.h = gb->h;
 										release_buffer(gb);
@@ -1125,6 +1127,7 @@ void sdl_video_event_thread(void *data)
 										src.h = list->rect.height;
 										if (sdl.QueryTexture(texture, NULL, NULL, &tw, &th) != 0)
 											fprintf(stderr, "Unable to query texture (%s)\n", sdl.GetError());
+										sdl.RenderClear(renderer);
 										if (sdl.LockTexture(texture, &src, &pixels, &pitch) != 0)
 											fprintf(stderr, "Unable to lock texture (%s)\n", sdl.GetError());
 										if (pitch != list->rect.width * sizeof(list->data[0])) {
@@ -1144,23 +1147,22 @@ void sdl_video_event_thread(void *data)
 											memcpy(pixels, list->data, list->rect.width * ch * sizeof(list->data[0]));
 										}
 										sdl.UnlockTexture(texture);
-										dst.w = cvstat.winwidth;
-										dst.h = cvstat.winheight;
+										dst.w = lvstat.winwidth;
+										dst.h = lvstat.winheight;
 										// Get correct aspect ratio for dst...
-										aspect_fix(&dst.w, &dst.h, cvstat.aspect_width, cvstat.aspect_height);
-										dst.x = (cvstat.winwidth - dst.w) / 2;
-										dst.y = (cvstat.winheight - dst.h) / 2;
+										aspect_fix(&dst.w, &dst.h, lvstat.aspect_width, lvstat.aspect_height);
+										dst.x = (lvstat.winwidth - dst.w) / 2;
+										dst.y = (lvstat.winheight - dst.h) / 2;
 									}
 									if (sdl.RenderCopy(renderer, texture, &src, &dst))
 										fprintf(stderr, "RenderCopy() failed! (%s)\n", sdl.GetError());
+									sdl.RenderPresent(renderer);
 								}
 								bitmap_drv_free_rect(list);
 							}
-							sdl.RenderPresent(renderer);
 						}
 
 						pthread_mutex_unlock(&win_mutex);
-						pthread_mutex_unlock(&vstatlock);
 						break;
 					case SDL_USEREVENT_SETNAME:
 						pthread_mutex_lock(&win_mutex);