qga: fix -Wsometimes-uninitialized windows warning

Reported by clang, but not gcc.

[5123/5678] Compiling C object qga/qemu-ga.exe.p/commands-windows-ssh.c.obj
FAILED: qga/qemu-ga.exe.p/commands-windows-ssh.c.obj
"cc" "-Iqga/qemu-ga.exe.p" "-Iqga" "-I../qga" "-I." "-Iqapi" "-Itrace" "-Iui" "-Iui/shader" "-IC:/msys64/clangarm64/include/glib-2.0" "-IC:/msys64/clangarm64/lib/glib-2.0/include" "-fdiagnostics-color=auto" "-Wall" "-Winvalid-pch" "-Werror" "-std=gnu11" "-O2" "-g" "-fstack-protector-strong" "-Wempty-body" "-Wendif-labels" "-Wexpansion-to-defined" "-Wformat-security" "-Wformat-y2k" "-Wignored-qualifiers" "-Winit-self" "-Wmissing-format-attribute" "-Wmissing-prototypes" "-Wnested-externs" "-Wold-style-definition" "-Wredundant-decls" "-Wstrict-prototypes" "-Wtype-limits" "-Wundef" "-Wvla" "-Wwrite-strings" "-Wno-gnu-variable-sized-type-not-at-end" "-Wno-initializer-overrides" "-Wno-missing-include-dirs" "-Wno-psabi" "-Wno-shift-negative-value" "-Wno-string-plus-int" "-Wno-tautological-type-limit-compare" "-Wno-typedef-redefinition" "-Wthread-safety" "-iquote" "." "-iquote" "C:/w/qemu" "-iquote" "C:/w/qemu/include" "-iquote" "C:/w/qemu/host/include/aarch64" "-iquote" "C:/w/qemu/host/include/generic" "-iquote" "C:/w/qemu/tcg/aarch64" "-D_GNU_SOURCE" "-D_FILE_OFFSET_BITS=64" "-D_LARGEFILE_SOURCE" "-fno-strict-aliasing" "-fno-common" "-fwrapv" "-fno-pie" "-ftrivial-auto-var-init=zero" "-fzero-call-used-regs=used-gpr" -MD -MQ qga/qemu-ga.exe.p/commands-windows-ssh.c.obj -MF "qga/qemu-ga.exe.p/commands-windows-ssh.c.obj.d" -o qga/qemu-ga.exe.p/commands-windows-ssh.c.obj "-c" ../qga/commands-windows-ssh.c
../qga/commands-windows-ssh.c:383:9: error: variable 'userPSID' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
  383 |     if (!create_acl(userInfo, &pACL, errp)) {
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../qga/commands-windows-ssh.c:415:15: note: uninitialized use occurs here
  415 |     LocalFree(userPSID);
      |               ^~~~~~~~
../qga/commands-windows-ssh.c:383:5: note: remove the 'if' if its condition is always false
  383 |     if (!create_acl(userInfo, &pACL, errp)) {
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  384 |         goto error;
      |         ~~~~~~~~~~~
  385 |     }
      |     ~
../qga/commands-windows-ssh.c:380:18: note: initialize the variable 'userPSID' to silence this warning
  380 |     PSID userPSID;
      |                  ^
      |                   = NULL
1 error generated.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
Link: https://lore.kernel.org/r/20241031040426.772604-6-pierrick.bouvier@linaro.org
Signed-off-by: Konstantin Kostiuk <kkostiuk@redhat.com>
diff --git a/qga/commands-windows-ssh.c b/qga/commands-windows-ssh.c
index 6a642e3..df45c17 100644
--- a/qga/commands-windows-ssh.c
+++ b/qga/commands-windows-ssh.c
@@ -377,7 +377,7 @@
 static bool set_file_permissions(PWindowsUserInfo userInfo, Error **errp)
 {
     PACL pACL = NULL;
-    PSID userPSID;
+    PSID userPSID = NULL;
 
     /* Creates the access control structure */
     if (!create_acl(userInfo, &pACL, errp)) {