vrend: Check resource creation more thoroughly

While we are at it:
  - free memory if texture allocation fails

Closes #144
Closes #145
Closes #146

v2: Move the error string creation to extra patch (Emil)
v3: Fix whitespace errors (Emil) and one logic error

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>