[CORE] Fix some logic errors reported in #4214

[zengdage]

1. Preserve state across spaces and %m modifiers.

2. Initialize GVariant parser state(tmp) for a and @ formats.

3. Advance the st only when an argument is read from stack.

4. Ignore NULL in XCB display registrations.

5. Fix space handling in the 32-bit wide scanf parser.

[ptitSeb]

I'l validate this one next week, after my vacaccions, so next week.

[zengdage]

Test case as follow, previously these programs failed and this pr makes them run properly.

//   gcc $(pkg-config --cflags glib-2.0) -O1 myalign_fix.c -o myalign_fix $(pkg-config --libs glib-2.0)

#include <stdio.h>
#include <string.h>
#include <wchar.h>
#include <glib.h>

static int failures;
static int total;

static void check(const char* name, const char* got, const char* expected)
{
    ++total;
    if (strcmp(got, expected) != 0) {
        printf("[FAIL] %s: got \"%s\", expected \"%s\"\n", name, got, expected);
        ++failures;
    } else {
        printf("[PASS] %s: \"%s\"\n", name, got);
    }
}

static void check_variant(const char* name, GVariant* v, const char* expected)
{
    if (v) {
        gchar* s = g_variant_print(v, TRUE);
        check(name, s, expected);
        g_free(s);
        g_variant_unref(v);
    } else {
        printf("[FAIL] %s: NULL\n", name);
        ++failures;
        ++total;
    }
}

int main(void)
{
    char buf[64];

    snprintf(buf, sizeof(buf), "[% d][% 6d]", 7, 8);
    check("printf % d", buf, "[ 7][     8]");

    /* @i as 6th arg (first from stack) */
    check_variant("overflow @i",
        g_variant_new("(iiiii@i)", 1, 2, 3, 4, 5, g_variant_new("i", 42)),
        "(1, 2, 3, 4, 5, 42)");

    /* two @i on stack — second relies on tmp reset */
    check_variant("overflow @i@i",
        g_variant_new("(iiiii@i@i)", 1, 2, 3, 4, 5,
            g_variant_new("i", 10), g_variant_new("i", 20)),
        "(1, 2, 3, 4, 5, 10, 20)");

    /* @(ii) on stack — exercises tmp nesting in state 3 */
    check_variant("overflow @(ii)",
        g_variant_new("(iiiii@(ii))", 1, 2, 3, 4, 5,
            g_variant_new("(ii)", 6, 7)),
        "(1, 2, 3, 4, 5, (6, 7))");

    /* ai as 6th arg — exercises state 1 in overflow */
    GVariantBuilder* b = g_variant_builder_new(G_VARIANT_TYPE("ai"));
    g_variant_builder_add(b, "i", 8);
    g_variant_builder_add(b, "i", 9);
    check_variant("overflow ai",
        g_variant_new("(iiiiiai)", 1, 2, 3, 4, 5, b),
        "(1, 2, 3, 4, 5, [8, 9])");
    g_variant_builder_unref(b);

    printf("\n%d passed, %d failed\n", total - failures, failures);
    return failures != 0;
}