Ticket #1906: edit: crash on file open whoen some Syntax files are absent (reported by pavlinux)

valgrind log snippet: (from here http://pavlinux.ru/vgmc.log)

> ==26750== HEAP SUMMARY:
> ==26750==     in use at exit: 0 bytes in 0 blocks
> ==26750==   ==26749== Invalid free() / delete / delete[]
> ==26749==    at 0x4A06DD8: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==26749==    by 0x48B5F9: edit_read_syntax_rules (syntax.c:766)
> ==26749==    by 0x48CDA7: edit_read_syntax_file (syntax.c:1140)
> ==26749==    by 0x48D06D: edit_load_syntax (syntax.c:1219)
> ==26749==    by 0x4762F6: edit_init (edit.c:834)
> ==26749==    by 0x4858FC: edit_file (editwidget.c:241)
> ==26749==    by 0x44D017: do_edit_at_line (cmd.c:304)
> ==26749==    by 0x44D098: do_edit (cmd.c:324)
> ==26749==    by 0x44D10E: edit_cmd (cmd.c:331)
> ==26749==    by 0x46C2E4: midnight_execute_cmd (main.c:1193)
> ==26749==    by 0x46CD41: midnight_callback (main.c:1690)
> ==26749==    by 0x4353F4: buttonbar_call (widget.c:2654)
> ==26749==  Address 0x60f8e10 is 0 bytes inside a block of size 30 free'd
> ==26749==    at 0x4A06DD8: free (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
> ==26749==    by 0x48B32C: open_include_file (syntax.c:705)
> ==26749==    by 0x48B6E8: edit_read_syntax_rules (syntax.c:784)
> ==26749==    by 0x48CDA7: edit_read_syntax_file (syntax.c:1140)
> ==26749==    by 0x48D06D: edit_load_syntax (syntax.c:1219)
> ==26749==    by 0x4762F6: edit_init (edit.c:834)
> ==26749==    by 0x4858FC: edit_file (editwidget.c:241)
> ==26749==    by 0x44D017: do_edit_at_line (cmd.c:304)
> ==26749==    by 0x44D098: do_edit (cmd.c:324)
> ==26749==    by 0x44D10E: edit_cmd (cmd.c:331)
> ==26749==    by 0x46C2E4: midnight_execute_cmd (main.c:1193)
> ==26749==    by 0x46CD41: midnight_callback (main.c:1690)

We see doublefree memory corruption here, introduced by spurious 'g_free(error_file_name)'
of changeset:0c17219b2ab5cb5fe2e73f8d7cc9c11c755a3ae4 (syntax.c file)

The rest of code seems to store real syntax file name there.

Making code the same as part above: don't free 'error_file_name'

Signed-off-by: Sergei Trofimovich <slyfox@inbox.ru>

edit/syntax.c

@@ -693,11 +693,10 @@ static FILE *open_include_file (const char *filename)
     g_free (error_file_name);
     error_file_name = g_strconcat (mc_home, PATH_SEP_STR, "syntax", PATH_SEP_STR,
 				   filename, (char *) NULL);
-
-    if ((f = fopen (error_file_name, "r"))) {
-	g_free (error_file_name);
+    f = fopen (error_file_name, "r");
+    if (f)
 	return f;
-    }
+
     g_free (error_file_name);
     error_file_name = g_strconcat (mc_home_alt, PATH_SEP_STR "syntax" PATH_SEP_STR,
 				   filename, (char *) NULL);