gp_ir/from_glsl: fix structures inside of structures

I forgot to add this line when copying this from the PP code.
gp_ir/from_glsl: fix segfault in the offset calculation code

out_indirect was never initialized to NULL in the base case of
calf_deref_offset, so we were using whatever garbage memory that was
passed in.
pp_hir/from_glsl: fix segfault in the offset calculation code

This is a port of the previous commit to the PP code.
from_glsl: fix for calculating matrix dereference offsets

The same logic was broken in both the PP and GP cases, and the fix is
also the same.