xkb/servermd: fix bit shifting by CWE-190 Integer Overflow or Wraparound

[GermanAizek]

Continue working prev PR here: https://github.com/X11Libre/xserver/pull/22

References:

• https://cwe.mitre.org/data/definitions/190.html

Example real CVE vulns with Integer Overflow:

• https://nvd.nist.gov/vuln/detail/CVE-2022-49748
• https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=08245672cdc6505550d1a5020603b0a8d4a6dcc7

[metux]

Needs a rebase against master - I had to rewrite history (see mail)

[GermanAizek]

Needs a rebase against master - I had to rewrite history (see mail) Okay, I got it