Skip video playback in HeadlessMode

play_movie() only early-outs for demo playback, but SVidPlayBegin
requires the SDL video subsystem that HeadlessMode intentionally never
initializes, so any real-time (non-demo) headless session crashes on
the first movie: the Lazarus in-game movie (gendata\fprst3.smk) and
the ending cinematics when Diablo dies. Mirror the existing
demo::IsRunning() early-out; the surrounding fade/redraw paths are
already headless-safe, and this one guard covers every callsite
(intro logos, Lazarus, victory/ending, credits loop).

No behavior change in graphical builds.

Source/movie.cpp

@@ -21,6 +21,7 @@
 #include "engine/demomode.h"
 #include "engine/events.hpp"
 #include "engine/sound.h"
+#include "headless_mode.hpp"
 #include "hwcursor.hpp"
 #include "storm/storm_svid.h"
 #include "utils/display.h"
@@ -38,6 +39,11 @@ void play_movie(const char *pszMovie, bool userCanClose)
 	if (demo::IsRunning())
 		return;
 
+	// Video playback requires the SDL video subsystem, which HeadlessMode
+	// intentionally does not initialize.
+	if (HeadlessMode)
+		return;
+
 	movie_playing = true;
 
 	sound_disable_music(true);