vbo: fix crash in vbo_exec_bind_arrays()

When a vertex shader uses generic vertex attribute 0, but not gl_Vertex,
we need to set attribute[16] to point to attribute[0].  We were setting the
attribute size, but not the pointer.

Fixes crash in glsl/multitex.c when using the VertCoord attribute instead
of gl_Vertex.

src/mesa/vbo/vbo_exec_draw.c

@@ -185,6 +185,7 @@ static void vbo_exec_bind_arrays( GLcontext *ctx )
           (ctx->VertexProgram._Current->Base.InputsRead & VERT_BIT_GENERIC0)) {
          exec->vtx.inputs[16] = exec->vtx.inputs[0];
          exec->vtx.attrsz[16] = exec->vtx.attrsz[0];
+         exec->vtx.attrptr[16] = exec->vtx.attrptr[0];
          exec->vtx.attrsz[0] = 0;
       }
       break;