glsl/ast: Check that geometry shader interface block inputs are arrays.
glsl/ast: Fix assertion failure when GS input declared as non-array.

Previously, if a geometry shader input was declared as a non-array, we
would flag the proper compiler error, but then before we got a chance
to report it to the client, handle_geometry_shader_input_decl() would
assertion fail.

With this patch, handle_geometry_shader_input_decl() ignores
non-arrays.
glsl/ast: Don't perform GS input array checks on non-inputs.

Previously, we were accidentally calling
handle_geometry_shader_input_decl() on non-input interface block
declarations, resulting in bogus error checking.