renderer: handle illegal so values better

This stops the guest from crashing the parser here,
if it gives us so entries that are invalid.

src/vrend_renderer.c

@@ -644,18 +644,19 @@ static void set_stream_out_varyings(int prog_id, struct vrend_shader_info *sinfo
    struct pipe_stream_output_info *so = &sinfo->so_info;
    char *varyings[PIPE_MAX_SHADER_OUTPUTS];
    int i;
-   
+   int n_outputs = 0;
    if (!so->num_outputs)
       return;
 
    for (i = 0; i < so->num_outputs; i++) {
-      varyings[i] = strdup(sinfo->so_names[i]);
+      if (sinfo->so_names[i])
+	 varyings[n_outputs++] = strdup(sinfo->so_names[i]);
    }
 
-   glTransformFeedbackVaryings(prog_id, so->num_outputs,
+   glTransformFeedbackVaryings(prog_id, n_outputs,
                                (const GLchar **)varyings, GL_INTERLEAVED_ATTRIBS_EXT);
 
-   for (i = 0; i < so->num_outputs; i++)
+   for (i = 0; i < n_outputs; i++)
       if (varyings[i])
          free(varyings[i]);
 }

src/vrend_shader.c

@@ -759,7 +759,10 @@ static int emit_so_movs(struct dump_ctx *ctx)
          writemask[0] = 0;
 
       if (ctx->so->output[i].num_components == 4 && writemask[0] == 0 && !(ctx->outputs[ctx->so->output[i].register_index].name == TGSI_SEMANTIC_CLIPDIST)) {
-         ctx->so_names[i] = strdup(ctx->outputs[ctx->so->output[i].register_index].glsl_name);
+	 if (ctx->so->output[i].register_index > ctx->num_outputs)
+	    ctx->so_names[i] = NULL;
+	 else
+	    ctx->so_names[i] = strdup(ctx->outputs[ctx->so->output[i].register_index].glsl_name);
          ctx->write_so_outputs[i] = false;
 
       } else {