glsl: Add field initializers for glsl_struct_field default constructor

This helps valgrind when encode_type_to_blob is used.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/glsl_types.h

@@ -1045,6 +1045,13 @@ struct glsl_struct_field {
    }
 
    glsl_struct_field()
+      : type(NULL), name(NULL), location(0), offset(0), xfb_buffer(0),
+        xfb_stride(0), interpolation(0), centroid(0),
+        sample(0), matrix_layout(0), patch(0),
+        precision(0), memory_read_only(0),
+        memory_write_only(0), memory_coherent(0), memory_volatile(0),
+        memory_restrict(0), image_format(0), explicit_xfb_buffer(0),
+        implicit_sized_array(0)
    {
       /* empty */
    }