interpolation: correct camera room number

This fixes some black screen moments by simplifying the room number on
the camera. This is always standardized when Room_GetFloor is called
against the actual camera position, so we needn't track it.

Resolves LostArtefacts#1240.
Resolves LostArtefacts#1241.
Resolves LostArtefacts#1243.

src/game/game/game_draw.c

@@ -19,7 +19,7 @@ void Game_DrawScene(bool draw_overlay)
     Camera_Apply();
 
     if (g_Objects[O_LARA].loaded) {
-        Room_DrawAllRooms(g_Camera.interp.result.room_num);
+        Room_DrawAllRooms(g_Camera.interp.room_num);
         if (draw_overlay) {
             Overlay_DrawGameInfo();
         } else {

src/game/interpolation.c

@@ -70,11 +70,11 @@ void Interpolation_Commit(void)
         INTERPOLATE(&g_Camera, target.y, ratio, 512);
         INTERPOLATE(&g_Camera, target.z, ratio, 512);
 
-        g_Camera.interp.result.room_num = g_Camera.interp.prev.room_num;
+        g_Camera.interp.room_num = g_Camera.pos.room_number;
         Room_GetFloor(
             g_Camera.interp.result.pos.x,
             g_Camera.interp.result.pos.y + g_Camera.interp.result.shift,
-            g_Camera.interp.result.pos.z, &g_Camera.interp.result.room_num);
+            g_Camera.interp.result.pos.z, &g_Camera.interp.room_num);
     }
 
     INTERPOLATE_ROT(&g_Lara.left_arm, rot.x, ratio, PHD_45);
@@ -146,7 +146,6 @@ void Interpolation_Remember(void)
         REMEMBER(&g_Camera, target.x);
         REMEMBER(&g_Camera, target.y);
         REMEMBER(&g_Camera, target.z);
-        g_Camera.interp.prev.room_num = g_Camera.pos.room_number;
     }
 
     REMEMBER(&g_Lara.left_arm, rot.x);

src/global/types.h

@@ -1856,8 +1856,8 @@ typedef struct CAMERA_INFO {
             XYZ_32 target;
             XYZ_32 pos;
             int32_t shift;
-            int16_t room_num;
         } result, prev;
+        int16_t room_num;
     } interp;
 } CAMERA_INFO;