mesa: fix target error checking in glGetTexLevelParameter

mesa: fix target error checking in glGetTexLevelParameter

With non-dsa functions we need to do target error checking before
_mesa_get_current_tex_object which would just call _mesa_problem without
raising GL_INVALID_ENUM error. In other places of Mesa, target gets checked
before this call.

Fixes failures in:
   ES31-CTS.texture_storage_multisample.APIGLGetTexLevelParameterifv.*

v2: do the target check also for dsa functions (Timothy)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Timothy Arceri <t_arceri@yahoo.com.au>