mesa: fix multisampling proxy textures not being queryable

The code that checks if some texture target is valid for
glGetTexLevelParameter*() was not programmed to check for multisampling
proxy textures.  This made it impossible(?) to use the proxy textures
for their intended purpose as glGetTexLevelParameter*() would just fail
on you.

Reviewed-by: Brian Paul <brianp@vmware.com>

Cc: mesa-stable@lists.freedesktop.org

src/mesa/main/texparam.c

@@ -1048,6 +1048,8 @@ legal_get_tex_level_parameter_target(struct gl_context *ctx, GLenum target)
       return ctx->API == API_OPENGL_CORE && ctx->Version >= 31;
    case GL_TEXTURE_2D_MULTISAMPLE:
    case GL_TEXTURE_2D_MULTISAMPLE_ARRAY:
+   case GL_PROXY_TEXTURE_2D_MULTISAMPLE:
+   case GL_PROXY_TEXTURE_2D_MULTISAMPLE_ARRAY:
       return ctx->Extensions.ARB_texture_multisample;
    default:
       return GL_FALSE;