libpayload: curses: Only call `serial_set_color()` with initialized values

Building nvramcui with i386-elf-gcc (coreboot toolchain
v2021-04-06_7014f8258e) 8.3.0 and Link Time Optimization (LTO) enabled
in libpayload (`CONFIG_LP_LTO=y`) fails with the error below.

        LPGCC      nvramcui.bin
    curses/PDCurses/pdcurses/refresh.c: In function 'wrefresh':
    curses/pdcurses-backend/pdcdisp.c:217:4: error: 'bg' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    curses/pdcurses-backend/pdcdisp.c:214:18: note: 'bg' was declared here
    curses/pdcurses-backend/pdcdisp.c:217:4: error: 'fg' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    curses/pdcurses-backend/pdcdisp.c:214:14: note: 'fg' was declared here
    lto1: all warnings being treated as errors
    lto-wrapper: fatal error: i386-elf-gcc returned 1 exit status
    compilation terminated.
    /opt/xgcc/lib/gcc/i386-elf/8.3.0/../../../../i386-elf/bin/ld.bfd: error: lto-wrapper failed
    collect2: error: ld returned 1 exit status

`pair_content()` returns in case `PAIR_NUMBER(attr)` is invalid, so
guard the usage of `serial_set_color()`.

    if (pair < 0 || pair >= COLOR_PAIRS || !fg || !bg)
        return ERR;

Note, building with x86_64-linux-gnu-gcc-10 (Debian 10.2.1-6) 10.2.1
20210110 does *not* fail.

Change-Id: Ic63e34f2b5bc9f826db37597bebc6b20542481d7
Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51914
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

0 files changed, 0 insertions, 0 deletions