Fix freeing the uninitialised variable

[mikhainin]

Even though, we initialise "space_string" with NULL, we goto schema_space_value_free() before this statement.

[mikhainin]

The problem was found by Polaris. A similar thing may be reported by Clang:

~/tmp/hello via C v14.0.3-clang via △ v3.25.2 on ☁️    🕙 46ms
❯ cat hello.c
void foo(int x) {
    (void)x;
}

void bar(void) {
    goto aaaa;
    int x = 10;
aaaa:
    foo(x);
}

~/tmp/hello via C v14.0.3-clang via △ v3.25.2 on ☁️    🕙 43ms
❯ cc -Wall -Wextra -pedantic-errors -c hello.c
hello.c:10:2: error: no newline at end of file [-Werror,-Wnewline-eof]
}
 ^
hello.c:9:6: warning: variable 'x' is uninitialized when used here [-Wuninitialized]
        foo(x);
            ^
hello.c:7:2: note: variable 'x' is declared here
        int x = 10;
        ^
1 warning and 1 error generated.

~/tmp/hello via C v14.0.3-clang via △ v3.25.2 on ☁️    🕙 43ms
❯

[Totktonada]

Looks valid. Thank you!