Clear MovieSession._queuedMovie if rom load fails (resolves #3582)

for #3582, `MovieSession.QueuedCoreName`, which gets passed to `RomLoader`,
evaluated to a nonexistent core name and couldn't be cleared

Author: YoshiRulz

src/BizHawk.Client.Common/movie/MovieSession.cs

@@ -261,6 +261,9 @@ public void RunQueuedMovie(bool recordMode, IEmulator emulator)
 			}
 		}
 
+		public void AbortQueuedMovie()
+			=> _queuedMovie = null;
+
 		public void StopMovie(bool saveChanges = true)
 		{
 			if (Movie.IsActive())

src/BizHawk.Client.Common/movie/interfaces/IMovieSession.cs

@@ -84,6 +84,9 @@ public interface IMovieSession
 		/// </summary>
 		void RunQueuedMovie(bool recordMode, IEmulator emulator);
 
+		/// <summary>clears the queued movie</summary>
+		void AbortQueuedMovie();
+
 		void StopMovie(bool saveChanges = true);
 
 		/// <summary>

src/BizHawk.Client.EmuHawk/MainForm.Movie.cs

@@ -48,6 +48,7 @@ public bool StartNewMovie(IMovie movie, bool record)
 			}
 			finally
 			{
+				MovieSession.AbortQueuedMovie();
 				Config.PreferredCores = oldPreferredCores;
 			}