Ticket #2195: Crash on search in viewed file after Parsed/Raw switching

View (F3) some file.
Switch Raw->Parse or Parse->Raw (F8).
Search any text, contained in the file.
Crash!

Signed-off-by: Slava Zanko <slavazanko@gmail.com>

src/viewer/nroff.c

@@ -278,7 +278,7 @@ mcview_nroff_seq_free (mcview_nroff_t ** nroff)
     if (nroff == NULL || *nroff == NULL)
         return;
     g_free (*nroff);
-    nroff = NULL;
+    *nroff = NULL;
 }
 
 /* --------------------------------------------------------------------------------------------- */