renderer: check for shader_text validity

Add a check for nonterminated string passed into the create_shader
code.

No point checking len <= 0, since it's a uint32_t.

Signed-off-by: Dave Airlie <airlied@redhat.com>

src/vrend_renderer.c

@@ -2929,6 +2929,9 @@ int vrend_create_shader(struct vrend_context *ctx,
    bool finished = false;
    int ret;
 
+   if (pkt_length == 0 || shd_text[pkt_length - 1] != '\0')
+      return EINVAL;
+
    if (type > PIPE_SHADER_COMPUTE)
       return EINVAL;