Allow NULL for cterm at exit...

src/conio/cterm.c

@@ -2538,6 +2538,7 @@ void cterm_end(struct cterminal *cterm)
 {
 	int i;
 
+	if(cterm) {
 		cterm_closelog(cterm);
 #ifdef CTERM_WITHOUT_CONIO
 		FREE_AND_NULL(BD->vmem);
@@ -2561,3 +2562,4 @@ void cterm_end(struct cterminal *cterm)
 		}
 		free(cterm);
 	}
+}