avoid other efforts if memory mapping fails

TSRM/tsrm_win32.c

@@ -671,10 +671,6 @@ TSRM_API void *shmat(int key, const void *shmaddr, int flags)
 		return (void*)-1;
 	}
 
-	shm->descriptor->shm_atime = time(NULL);
-	shm->descriptor->shm_lpid  = getpid();
-	shm->descriptor->shm_nattch++;
-
 	shm->addr = MapViewOfFileEx(shm->segment, FILE_MAP_ALL_ACCESS, 0, 0, 0, NULL);
 
 	err = GetLastError();
@@ -686,6 +682,10 @@ TSRM_API void *shmat(int key, const void *shmaddr, int flags)
 		return (void*)-1;
 	}
 
+	shm->descriptor->shm_atime = time(NULL);
+	shm->descriptor->shm_lpid  = getpid();
+	shm->descriptor->shm_nattch++;
+
 	return shm->addr;
 }