renderer: handle gaps in vertex shader inputs

We are seeing shaders with 0 and 2 inputs, but no 1, so we need
to handle gaps properly.

This fixes some regressions in drawpixels after some mesa changes
on the guest.

src/vrend_renderer.c

@@ -863,7 +863,9 @@ static struct vrend_linked_shader_program *add_shader_program(struct vrend_conte
       sprog->dual_src_linked = false;
 
    if (vrend_state.have_vertex_attrib_binding) {
-      for (i = 0; i < vs->sel->sinfo.num_inputs; i++) {
+      uint32_t mask = vs->sel->sinfo.attrib_input_mask;
+      while (mask) {
+         i = u_bit_scan(&mask);
          snprintf(name, 10, "in_%d", i);
          glBindAttribLocation(prog_id, i, name);
       }

src/vrend_shader.c

@@ -83,6 +83,7 @@ struct dump_ctx {
 
    int num_interps;
    int num_inputs;
+   uint32_t attrib_input_mask;
    struct vrend_shader_io inputs[32];
    int num_outputs;
    struct vrend_shader_io outputs[32];
@@ -245,6 +246,9 @@ iter_declaration(struct tgsi_iterate_context *iter,
    switch (decl->Declaration.File) {
    case TGSI_FILE_INPUT:
       i = ctx->num_inputs++;
+      if (iter->processor.Processor == TGSI_PROCESSOR_VERTEX) {
+         ctx->attrib_input_mask |= (1 << decl->Range.First);
+      }
       ctx->inputs[i].name = decl->Semantic.Name;
       ctx->inputs[i].sid = decl->Semantic.Index;
       ctx->inputs[i].interpolate = decl->Interp.Interpolate;
@@ -2403,6 +2407,7 @@ char *vrend_convert_shader(struct vrend_shader_cfg *cfg,
    sinfo->glsl_ver = ctx.glsl_ver_required;
    sinfo->gs_out_prim = ctx.gs_out_prim;
    sinfo->so_names = ctx.so_names;
+   sinfo->attrib_input_mask = ctx.attrib_input_mask;
    return glsl_final;
  fail:
    free(ctx.glsl_main);

src/vrend_shader.h

@@ -45,7 +45,7 @@ struct vrend_shader_info {
    int glsl_ver;
    uint32_t shadow_samp_mask;
    int gs_out_prim;
-
+   uint32_t attrib_input_mask;
    struct pipe_stream_output_info so_info;
 
    struct vrend_interp_info *interpinfo;