preproc: Free token's text if only it has been modified

https://bugzilla.nasm.us/show_bug.cgi?id=3392414

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

asm/preproc.c

@@ -1280,8 +1280,8 @@ static char *detoken(Token * tlist, bool expand_locals)
                     t->text = nasm_zalloc(2);
                 } else
                     t->text = nasm_strdup(p);
+		nasm_free(q);
             }
-            nasm_free(q);
         }
 
         /* Expand local macros here and not during preprocessing */