Prevent UI thread deadlocking on Dispose()'ing rcheevos stuff

src/BizHawk.Client.EmuHawk/RetroAchievements/RCheevos.Http.cs

@@ -179,6 +179,14 @@ namespace BizHawk.Client.EmuHawk
 					return shouldRemove;
 				});
 			}
+
+			// typically I'd rather do this Dispose()
+			// but the Wait() semantics mean we can't do that on the UI thread
+			foreach (var request in _activeHttpRequests)
+			{
+				if (request is ImageRequest) continue; // THIS IS BAD, I KNOW (but don't want the user to wait for useless ImageRequests to finish)
+				request.Dispose(); // implicitly waits for the request to finish or timeout
+			}
 		}
 
 		private static async Task<byte[]> HttpGet(string url)

src/BizHawk.Client.EmuHawk/RetroAchievements/RCheevos.cs

@@ -226,13 +226,6 @@ namespace BizHawk.Client.EmuHawk
 			_isActive = false;
 			_httpThread.Join();
 
-			// the http thread is dead, so we can safely use _activeHttpRequests
-			foreach (var request in _activeHttpRequests)
-			{
-				if (request is ImageRequest) continue; // THIS IS BAD, I KNOW
-				request.Dispose(); // implicitly waits for the request to finish or timeout
-			}
-
 			_lib.rc_runtime_destroy(ref _runtime);
 			Stop();
 			_gameInfoForm.Dispose();