dix: avoid null ptr deref at doListFontsAndAliases

In the `doListFontsAndAliases` function in dixfonts.c, when a font alias
is encountered (`err == FontNameAlias`) as a result of
`list_next_font_or_alias` call, the code allocates memory for
`resolved` variable (`resolvedlen + 1` bytes) for storing target font
name. In this case, if the `malloc(resolvedlen + 1)` call fails,
`resolved` remains NULL.

Later, when check (`else if (err == FontNameAlias)`) is TRUE, the code
uses `memcpy` to copy nullable `resolved` into `tmp_pattern` without
checking if `resolved` is NULL, so there is a potential null ptr
dereference.

This commit replaces `malloc` with `XNFalloc` for allocating memory for
`resolved`. `XNFalloc` will internally check result of `malloc` and stop
program execution if allocation was failed, preventing potential NULL
dereferencing.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Mikhail Dmitrichenko <m.dmitrichenko222@gmail.com>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2114>

dix/dixfonts.c

@@ -630,8 +630,7 @@ doListFontsAndAliases(ClientPtr client, LFclosurePtr c)
                 }
                 if (err == FontNameAlias) {
                     free(resolved);
-                    resolved = calloc(1, resolvedlen + 1);
-                    if (resolved)
+                    resolved = XNFalloc(resolvedlen + 1);
                     memcpy(resolved, tmpname, resolvedlen + 1);
                 }
             }