jak3: fix zoom blur flashbang in retail (#4305)

When `do_zoom_blur` sets up its draw, it doesn't update the blend
settings, so it ends up inheriting the previous values.

In retail mode, the previous draw is from a texture animation, which
sets up the blend in a specific way that causes it to draw a white
texture over the screen. In debug mode, right before the zoom blur is
drawn, the debug text is drawn, which modifies the blend settings to
something that makes the blur look as it should.

Closes #4206

game/graphics/opengl_renderer/BlitDisplays.cpp

@@ -167,6 +167,8 @@ void BlitDisplays::do_zoom_blur(SharedRenderState* render_state, ScopedProfilerN
   // GL Setup
   glDisable(GL_DEPTH_TEST);
   glEnable(GL_BLEND);
+  glBlendFuncSeparate(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ZERO);
+  glBlendEquation(GL_FUNC_ADD);
   glBindTexture(GL_TEXTURE_2D, m_blur_old_copier.texture());
 
   // draw old image