OGL: Disable scissor test when calling glBlitFramebuffer()

glBlitFramebuffer() does not bypass the scissor test, which meant that
part of texture copies (e.g. XFB) could have been clipped when running
under OpenGL ES, as glCopyImageSubData() is not supported.

Source/Core/VideoBackends/OGL/OGLTexture.cpp

@@ -234,6 +234,9 @@ void OGLTexture::BlitFramebuffer(OGLTexture* srcentry, const MathUtil::Rectangle
                               dst_layer);
   }
 
+  // glBlitFramebuffer is still affected by the scissor test, which is enabled by default.
+  glDisable(GL_SCISSOR_TEST);
+
   glBlitFramebuffer(src_rect.left, src_rect.top, src_rect.right, src_rect.bottom, dst_rect.left,
                     dst_rect.top, dst_rect.right, dst_rect.bottom, GL_COLOR_BUFFER_BIT, GL_NEAREST);
 
@@ -252,6 +255,9 @@ void OGLTexture::BlitFramebuffer(OGLTexture* srcentry, const MathUtil::Rectangle
         0);
   }
 
+  // The default state for the scissor test is enabled. We don't need to do a full state
+  // restore, as the framebuffer and scissor test are the only things we changed.
+  glEnable(GL_SCISSOR_TEST);
   FramebufferManager::SetFramebuffer(0);
 }