wined3d: Also update the "src_texture_gl" pointer when using a staging texture in the blitter.

dlls/wined3d/arb_program_shader.c

@@ -7841,6 +7841,7 @@ static DWORD arbfp_blitter_blit(struct wined3d_blitter *blitter, enum wined3d_bl
                 src_texture, src_sub_resource_idx, &upload_box);
 
         src_texture = staging_texture;
+        src_texture_gl = wined3d_texture_gl(src_texture);
         src_sub_resource_idx = 0;
     }
     else if (wined3d_settings.offscreen_rendering_mode != ORM_FBO

dlls/wined3d/glsl_shader.c

@@ -13258,6 +13258,7 @@ static DWORD glsl_blitter_blit(struct wined3d_blitter *blitter, enum wined3d_bli
                 src_texture, src_sub_resource_idx, &upload_box);
 
         src_texture = staging_texture;
+        src_texture_gl = wined3d_texture_gl(src_texture);
         src_sub_resource_idx = 0;
     }
     else if (wined3d_settings.offscreen_rendering_mode != ORM_FBO

dlls/wined3d/surface.c

@@ -2213,6 +2213,7 @@ static DWORD ffp_blitter_blit(struct wined3d_blitter *blitter, enum wined3d_blit
                 src_texture, src_sub_resource_idx, &upload_box);
 
         src_texture = staging_texture;
+        src_texture_gl = wined3d_texture_gl(src_texture);
         src_sub_resource_idx = 0;
     }
     else