compiler/glsl: Initialize local variable to zero to fix MSVC RTC error

Without this, we get a run-time error about using an uninitialized
variable.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6221>
diff --git a/src/compiler/glsl/ast_to_hir.cpp b/src/compiler/glsl/ast_to_hir.cpp
index c406ae2..6c0c3b6 100644
--- a/src/compiler/glsl/ast_to_hir.cpp
+++ b/src/compiler/glsl/ast_to_hir.cpp
@@ -8007,7 +8007,7 @@
       return NULL;
    }
 
-   unsigned qual_xfb_offset;
+   unsigned qual_xfb_offset = 0;
    if (layout.flags.q.explicit_xfb_offset) {
       if (!process_qualifier_constant(state, &loc, "xfb_offset",
                                       layout.offset, &qual_xfb_offset)) {
@@ -8015,7 +8015,7 @@
       }
    }
 
-   unsigned qual_xfb_stride;
+   unsigned qual_xfb_stride = 0;
    if (layout.flags.q.explicit_xfb_stride) {
       if (!process_qualifier_constant(state, &loc, "xfb_stride",
                                       layout.xfb_stride, &qual_xfb_stride)) {