Fix crash (segfault) in etags on generating tags for Erlang files

* lib-src/etags.c: Set allocated and lastlen to zero, after
freeing last ptr in Erlang_functions to prevent dereferencing NULL
pointer (bug#45122).

Copyright-paperwork-exempt: yes

(cherry picked from commit 2d8f0364)

lib-src/etags.c

@@ -6062,6 +6062,7 @@ Erlang_functions (FILE *inf)
 	    {
 	      free (last);
 	      last = NULL;
+	      allocated = lastlen = 0;
 	    }
 	}
       else