main: Clear shader program data whenever ProgramBinary is called

main: Clear shader program data whenever ProgramBinary is called

The GL_ARB_get_program_binary extension spec says:

 "If ProgramBinary fails to load a binary, no error is generated, but
  any information about a previous link or load of that program object
  is lost."

v2:
 * Re-initialize shProg->data after clear. (Jordan)
   (Required after 6a72eba755fea15a0d97abb913a6315d9d32e274)

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>