use destructor attribute for W_Shutdown

makes sure this is always called in any case
also just simpler

src/sdl/i_system.cpp

@@ -1444,7 +1444,6 @@ void I_Quit(void)
 	if (myargmalloc)
 		free(myargv); // Deallocate allocated memory
 
-	W_Shutdown();
 	exit(0);
 }
 
@@ -1522,7 +1521,6 @@ FUNCIERROR void ATTRNORETURN I_Error(const char *error, ...)
 					"SRB2Kart V2 " VERSIONSTRING " Recursive Error",
 					buffer, NULL);
 
-			W_Shutdown();
 			exit(-1); // recursive errors detected
 		}
 	}
@@ -1570,8 +1568,6 @@ FUNCIERROR void ATTRNORETURN I_Error(const char *error, ...)
 	I_ShutdownSystem();
 	SDL_Quit();
 
-	W_Shutdown();
-
 #if defined (PARANOIA) || defined (DEVELOP)
 	*(volatile INT32 *)0 = 4; //Alam: Debug!
 #endif

src/w_wad.c

@@ -125,7 +125,7 @@ wadfile_t *wadfiles[MAX_WADFILES]; // 0 to numwadfiles-1 are valid
 // If not done on a Mac then open wad files
 // can prevent removable media they are on from
 // being ejected
-void W_Shutdown(void)
+DESTRUCTOR static void W_Shutdown(void)
 {
 	lumpnum_map_cleanup(&lumpnumcache);
 

src/w_wad.h

@@ -152,8 +152,6 @@ extern wadfile_t *wadfiles[MAX_WADFILES];
 
 // =========================================================================
 
-void W_Shutdown(void);
-
 // Opens a WAD file. Returns the FILE * handle for the file, or NULL if not found or could not be opened
 FILE *W_OpenWadFile(const char **filename, boolean useerrors);
 // Load and add a wadfile to the active wad files, returns numbers of lumps, INT16_MAX on error